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<pre class='metadata'>
Title: CSS Color Module Level 5
Shortname: css-color
Level: 5
Status: ED
Prepare for TR: no
Group: csswg
TR: https://www.w3.org/TR/css-color-5/
ED: https://drafts.csswg.org/css-color-5/
Previous Version: https://www.w3.org/TR/2024/WD-css-color-5-20240229/
Work Status: exploring
!Delta Spec: yes
Editor: Chris Lilley, W3C, https://svgees.us/, w3cid 1438
Editor: Una Kravets, Google, https://una.im, w3cid 115525
Editor: Lea Verou, Invited Expert, https://lea.verou.me/about, w3cid 52258
Editor: Adam Argyle, Google, https://nerdy.dev, w3cid 112669
Abstract: This module extends CSS Color [[css-color-4]] to add color modification functions, custom color spaces (ICC profiles), contrast-color(), light-dark() and device-cmyk().
Repository: w3c/csswg-drafts
WPT Path Prefix: css/css-color/
WPT Display: open
</pre>
<pre class='ignored-specs'>
spec:css-color-3
</pre>
<pre class="link-defaults">
spec:css-color-4; type:dfn; text:color space
spec:css-color-4; type:dfn; text:gamut
spec:css-color-4; type:dfn; text:rectangular orthogonal color
spec:css-color-4; type:dfn; text:cylindrical polar color
spec:css-color-4; type:value; text:none
spec:css-color-4; type:value; text:srgb
spec:css-color-4; type:dfn; text:modern color syntax
spec:css-color-4; type:value; text:alpha-value
spec:css-values-5; type:value; text:color
spec:css-color-adjust-1; type:value; text:light
spec:css-color-adjust-1; type:value; text:dark
spec:css-color-4; type:value; text:rec2020
</pre>
<pre class=biblio>
{
"FOGRA39": {
"title": "ISO 12647-2:2004 / Amd 1, Offset commercial and specialty printing according to ISO 12647-2, paper type 1 or 2 (gloss or matte coated offset, 115 g/m²), screen frequency 60/cm ",
"publisher": "Forschungsgesellschaft Druck e.V. Graphic Technology Research Association",
"date": "2006",
"href": "https://www.color.org/chardata/FOGRA39.xalter"
},
"FOGRA51": {
"title": "ISO 12647-2:2013, Process control for the production of half-tone colour separations, proof and production printsPart 2: Offset lithographic processes, PS 1, premium coated, 115 g/m², moderate substrate fluorescence",
"publisher": "Forschungsgesellschaft Druck e.V. Graphic Technology Research Association",
"date": "2015",
"href": "https://www.color.org/chardata/fogra51.xalter"
},
"FOGRA55": {
"title": "CMYKOGV-based gamut exchange space",
"publisher": "Forschungsgesellschaft Druck e.V. Graphic Technology Research Association",
"date": "2021",
"href": "https://fogra.org/en/research/prepress-technology/multiprimary-printing-13003"
}
}
</pre>
<link rel="stylesheet" href="style.css" />
<style>
table.deltaE td {border: 4px solid white; padding: 6px; font-size: 1.4em; color: black;}
table.deltaE td.dE0 { background: rgb(68, 243, 91)}
table.deltaE td.dE1 { background: rgb(153, 243, 68)}
table.deltaE td.dE2 { background: rgb(217, 243, 68)}
table.deltaE td.dE3 { background: rgb(243, 240, 68)}
table.deltaE td.dE4 { background: rgb(243, 202, 68)}
table.deltaE td.dE5 { background: rgb(243, 103, 68); color: white}
table.deltaE th {text-align: center }
/* work-around for https://github.com/tabatkins/bikeshed/issues/1799 */
div.example, div.example pre {
overflow: visible;
}
div.example>a.self-link::before {
content: "¶";
}
</style>
<script>
document.addEventListener("DOMContentLoaded", ()=>{
for (let e of document.querySelectorAll(".swatch")) {
e.tabIndex = "0";
const swatchColor = getComputedStyle(e).getPropertyValue("--color");
if (!CSS.supports('color', swatchColor)) {
e.style.background = "repeating-linear-gradient(135deg, red 0, red 4px, white 4px, white 8px)";
e.setAttribute("title", "Your browser does not recognize this color value, so we can't preview it.");
}
}
});
</script>
Introduction {#intro}
=====================
<em>This section is not normative.</em>
This module adds the new functions
''contrast-color()'',
''color-mix()'' and ''light-dark()'',
and extends existing ones with [[#relative-colors|relative color syntax]].
It also extends the ''color()'' function
so that not only predefined color spaces,
but also custom color spaces defined by ICC profiles
(including calibrated CMYK)
can be used in CSS.
It also adds ''device-cmyk'',
a representation of
uncalibrated cmyk color.
<h2 id="color-syntax">The <<color>> syntax</h2>
Colors in CSS are represented by the <dfn export><<color>></dfn> type:
<pre class='prod'>
<color> = <<color-base>> | currentColor | <<system-color>> |
<<contrast-color()>> | <<device-cmyk()>> | <<light-dark()>>
<dfn><color-base></dfn> = <<hex-color>> | <<color-function>> | <<named-color>> | <<color-mix()>> | transparent
<dfn><color-function></dfn> = <<rgb()>> | <<rgba()>> |
<<hsl()>> | <<hsla()>> | <<hwb()>> |
<<lab()>> | <<lch()>> | <<oklab()>> | <<oklch()>> |
<<color()>>
</pre>
An <dfn export>absolute color</dfn>
is a <<color>> whose computed value
has an absolute, colorimetric interpretation.
This means that the value is not:
* ''currentColor'' (which depends on the value of the 'color' property)
* a <<system-color>> (which depends on the color mode)
* <<light-dark()>> (which depends on the color mode)
* <<contrast-color()>> (which depends on the color mode)
* <<device-cmyk()>> (which has no colorimetric basis)
Nor are any of those values used inside <<color-mix()>>
or in relative color syntax.
<!--
██ ██ ████ ██ ██
███ ███ ██ ██ ██
████ ████ ██ ██ ██
██ ███ ██ ██ ███
██ ██ ██ ██ ██
██ ██ ██ ██ ██
██ ██ ████ ██ ██
-->
<!--
https://caniuse.com/mdn-css_types_color_color-mix
-->
Mixing Colors: the ''color-mix()'' Function {#color-mix}
=====================================================
Web developers, design tools and design system developers
often use color functions to assist in scaling the design
of their component color relations.
With the increasing usage of design systems that support multiple platforms
and multiple user preferences, like the increased capability of Dark Mode in UI,
this becomes even more useful to not need to manually set color,
and to instead have a single source from which schemes are calculated.
<figure id="fig-chloropleth">
<p><img src="images/LC-picker-scale.png" alt="LC color picker" width=1168 height=1045 style="width: 40vmin"><br/>
<img src="images/LC-picker-map2.png" alt="chloropleth map of the US" width=1396 height=1014 style="width: 48vmin"></p>
<figcaption>Above, a color picker operating in CIE LCH space.
Here, a pair of colors are being used
to define a color scale
on the Chroma-Lightness plane (constant Hue).
Below, the color scale in use on a choropleth map.
</figcaption>
</figure>
<!-- from http://tristen.ca/hcl-picker/#/clh/8/267/0023A5/F8E0D6 -->
Currently Sass, calc() on HSL values, or PostCSS is used to do this.
However, preprocessors are unable to work on dynamically adjusted colors;
all current solutions are restricted to the sRGB gamut
and to the perceptual limitations of HSL
(colors are bunched up in the color wheel,
and two colors with visually different lightness,
like yellow and blue, can have the same HSL lightness).
To meet this need, the color-mix() function takes two <<color>> specifications
and returns the result of mixing them,
in a given <<color-space>>,
by a specified amount.
<pre class='prod'>
<dfn>color-mix()</dfn> = color-mix( <<color-interpolation-method>> , [ <<color>> && <<percentage [0,100]>>? ]#{2})
</pre>
<wpt>
parsing/color-computed-color-mix-function.html
parsing/color-valid-color-mix-function.html
</wpt>
<h3 id="color-mix-percent-norm">
Percentage Normalization
</h3>
Percentages are required to be in the range 0% to 100%. Negative percentages are specifically disallowed. The percentages are normalized as follows:
1. Let <var>p1</var> be the first percentage and <var>p2</var> the second one.
2. If both percentages are omitted, they each default to 50%
(an equal mix of the two colors).
3. Otherwise, if <var>p2</var> is omitted, it becomes 100% - <var>p1</var>
4. Otherwise, if <var>p1</var> is omitted, it becomes 100% - <var>p2</var>
5. Otherwise, if both are provided and add up to greater than 100%,
they are scaled accordingly so that they add up to 100%.
6. Otherwise, if both are provided and add up to less than 100%,
the sum is saved as an alpha multiplier.
If the sum is greater than zero,
they are then scaled accordingly so that they add up to 100%.
This means that
<var>p1</var> becomes <var>p1</var> / (<var>p1</var> + <var>p2</var>)
and
<var>p2</var> becomes <var>p2</var> / (<var>p1</var> + <var>p2</var>).
<wpt>
color-mix-percents-01.html
color-mix-percents-02.html
</wpt>
<div class="example" id="ex-mix-syntactic">
<!-- https://colorjs.io/notebook/?storage=https%3A%2F%2Fgist.github.com%2Fsvgeesus%2Fe37b01c449283352482d05fae52b9452 -->
These syntactic forms are thus all equivalent:
<pre class="lang-css">
color-mix(in lch, purple 50%, plum 50%)
color-mix(in lch, purple 50%, plum)
color-mix(in lch, purple, plum 50%)
color-mix(in lch, purple, plum)
color-mix(in lch, plum, purple)
color-mix(in lch, purple 80%, plum 80%)
</pre>
All produce a 50-50 mix of <span class="swatch" style="--color: purple"></span> purple and <span class="swatch" style="--color: plum"></span> plum,
in lch: <span class="swatch" style="--color: rgb(68.51%, 36.01%, 68.29%)"></span> lch(51.51% 52.21 325.8) which is <span class="swatch" style="--color: rgb(68.51%, 36.01%, 68.29%)"></span> rgb(68.51% 36.01% 68.29%).
However, this form is <em>not</em> the same, as the alpha is less than one:
<pre class="lang-css">
color-mix(in lch, purple 30%, plum 30%)
</pre>
This produces <span class="swatch" style="--color: rgb(68.51%, 36.01%, 68.29%, 0.6)"></span> lch(51.51% 52.21 325.8 / 0.6) which is <span class="swatch" style="--color: rgb(68.51%, 36.01%, 68.29%, 0.6)"></span> rgb(68.51% 36.01% 68.29% / 0.6).
</div>
<h3 id="color-mix-result">
Calculating the Result of color-mix
</h3>
After normalizing both percentages, the result is produced via the following algorithm:
1. If the alpha multiplier is zero, the result is ''transparent'', converted to the specified interpolation <<color-space>>
2. Otherwise, as described in [[css-color-4#interpolation]],
both colors are converted to the specified interpolation <<color-space>>,
taking into account any [=analogous components=].
3. Colors are then interpolated in the specified color space,
as described in [[css-color-4#interpolation]].
If the specified color space is a ''cylindrical-polar-color'' space,
then the <<hue-interpolation-method>> controls the
interpolation of hue, as described in
[[css-color-4#hue-interpolation]].
If no <<hue-interpolation-method>> is specified, it is as if
''shorter'' had been specified.
4. If an alpha multiplier was produced during percentage normalization,
the alpha component of the interpolated result is multiplied
by the alpha multiplier.
<wpt>
color-mix-basic-001.html
color-mix-missing-components.html
color-mix-non-srgb-001.html
parsing/color-computed-color-mix-function.html
parsing/color-invalid-color-mix-function.html
parsing/color-valid-color-mix-function.html
parsing/color-mix-out-of-gamut.html
/html/canvas/element/fill-and-stroke-styles/2d.fillStyle.colormix.html
/html/canvas/element/fill-and-stroke-styles/2d.fillStyle.colormix.currentcolor.html
/html/canvas/element/fill-and-stroke-styles/2d.strokeStyle.colormix.html
</wpt>
<!-- @@ Need WPT to test the sum to zero case, to generate transparent black
https://github.com/w3c/csswg-drafts/issues/11678#issuecomment-2686226875
-->
The result of mixing is the color at the specified percentage along the progression
of the second color to the first color.
Note: As a corollary, a percentage of 0% just returns the other color converted to the specified color space,
and a percentage of 100% returns the same color converted to the specified color space.
<div class="example" id="ex-mix-lch-peru40">
<!--
https://colorjs.io/notebook/?storage=https%3A%2F%2Fgist.github.com%2Fsvgeesus%2F2ddd7cf7cf822f2fb2bdc32faeb2b7f6
-->
This example produces a mixture of 40% <span class="swatch" style="--color: peru"></span> peru
and 60% <span class="swatch" style="--color: palegoldenrod"></span> palegoldenrod.
<pre class="lang-css">color-mix(in lch, peru 40%, palegoldenrod)</pre>
The mixing is done in ''lch'' color space.
Here is a top-down view, looking along the neutral L axis:
<figure id="fig-LCH-peru-goldenrod">
<object data="images/CH-mixing.svg" width=480 height=480>
<p>A mixture of two colors, and the mixed output.
We are looking down the CIE L axis onto the ab plane.
There are two axes, labelled <em>a</em> and <em>b</em>
which cross at the origin,
which is in the centre of the plot.</p>
</object>
<figcaption>Mixtures of peru and palegoldenrod in CIE LCH.
Peru has a hue angle, measured from the positive a axis,
of 63.677 degrees
while palegoldenrod has a hue angle of 98.834 degrees.
Peru has a chroma, or distance from the central neutral axis, of 54.011
while palegoldenrod has a chroma of 31.406.
All possible mixtures lie along the curve. A 40%/60% mixture is shown.
</figcaption>
</figure>
The calculation is as follows:
* <span class="swatch" style="--color: peru"></span> peru is lch(62.253% 54.011 63.677)
* <span class="swatch" style="--color: palegoldenrod"></span> palegoldenrod is lch(91.374% 31.406 98.834)
* the mixed lightness is 62.253 * 40/100 + 91.374 * (100-40)/100 = 79.7256
* the mixed chroma is 54.011 * 40/100 + 31.406 * (100-40)/100 = 40.448
* the mixed hue is 63.677 * 40/100 + 98.834 * (100-40)/100 = 84.771
* the mixed result is <span class="swatch" style="--color: rgb(87.416% 76.036% 47.637%)"></span> lch(79.7256% 40.448 84.771)
</div>
<div class="example" id="ex-mix-lch-teal65">
<!--
https://colorjs.io/notebook/?storage=https%3A%2F%2Fgist.github.com%2Fsvgeesus%2F2fb07e0a4eef97b0d0a1950f94ab3951
-->
This example produces the mixture of teal and olive,
in ''lch'' color space,
with each lch component being 65% of the value for teal
and 35% of the value for olive.
Note: interpolating on hue and chroma
keeps the intermediate colors
as saturated as the endpoint colors.
<pre class="lang-css">color-mix(in lch, teal 65%, olive);</pre>
<figure id="fig-LCH-teal-olive">
<object data="images/CH-mixing3.svg" width=500 height=500>
<p>A mixture of two colors, and the mixed output.
We are looking down the CIE L axis onto the ab plane.
There are two axes, labelled <em>a</em> and <em>b</em>
which cross at the origin,
which is in the centre of the plot.
</p>
</object>
<figcaption>Mixtures of teal and olive.
Teal has a hue angle, measured from the positive a axis,
of 196.4524 degrees
while olive has a hue angle of 99.5746 degrees.
Teal has a chroma, or distance from the central neutral axis, of 31.6903
while olive has a chroma of 56.8124.
Mixtures lie along the dashed curve. A 65%/35% mixture is shown.
</figcaption>
</figure>
The calculation is as follows:
* sRGB <span class="swatch" style="--color: teal"></span> teal (#008080) is lch(47.9855% 31.6903 196.4524)
* sRGB <span class="swatch" style="--color: olive"></span> olive (#808000) is lch(52.1496% 56.8124 99.5746)
* mixed lightness is 47.9855 * 0.65 + 52.1496 * 0.35 = 49.4429
* mixed chroma is 31.6903 * 0.65 + 56.8124 * 0.35 = 40.4830
* mixed hue is 196.4524 * 0.65 + 99.5746 * 0.35 = 162.5452
* mixed result is lch(49.4429% 40.4830 162.5452)
* which is a slightly-blueish green: <span class="swatch" style="--color: rgb(7.7377% 52.5730% 37.3213%)"></span> rgb(7.7377% 52.5730% 37.3213%)
</div>
<div class="example" id="ex-mix-zero-sum">
In this example, both percentages are zero, so their sum is also zero:
<pre class="lang-css">color-mix(in oklch, teal 0%, olive 0%);</pre>
Thus, the result is transparent black, in the ''oklch'' color space:<br>
<span class="swatch" style="--color: transparent"></span> oklch(0% 0 none / 0)
</div>
<h3 id="color-mix-color-space-effect">
Effect of Mixing Color Space on color-mix
</h3>
The choice of mixing color space can have a large effect on the end result.
<div class="example" id="ex-mix-colorspaces-black-white">
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This example is a 50% mix of white and black,
in three different color spaces.
<pre class="lang-css">
color-mix(in lch, white, black);
color-mix(in xyz, white, black);
color-mix(in srgb, white, black);
</pre>
The calculation is as follows:
* sRGB <span class="swatch" style="--color: white"></span> white (#FFF) is lch(100% 0 0)
* sRGB <span class="swatch" style="--color: black"></span> black (#000) is lch(0% 0 0)
* The mix in LCH is <span class="swatch" style="--color: rgb(47% 47% 47%)"></span> lch(50% 0 0)
* The mix in XYZ is <span class="swatch" style="--color: rgb(74% 74% 74%)"></span> lch(76% 0 0)
* The mix in sRGB is <span class="swatch" style="--color: rgb(50% 50% 50%)"></span> lch(53.4% 0 0)
The mix in LCH gives an L value of 50%,
a perfect mid gray, exactly as expected
(mixing in Lab would do the same,
as the Lightness axis is the same in LCH and Lab).
The mix in XYZ gives a result that is too light;
XYZ is linear-light but is not perceptually uniform.
The mix in sRGB gives a result that is a bit too light;
sRGB is neither perceptually uniform nor linear-light.
</div>
<div class="example" id="ex-mix-xyz">
This example produces the mixture of
the a red and a sky blue,
in ''xyz'' color space,
with the mixture being 75.23% of that of the red
(and thus, 24.77% of that of the blue).
<pre class="lang-css">color-mix(in xyz, rgb(82.02% 30.21% 35.02%) 75.23%, rgb(5.64% 55.94% 85.31%));</pre>
The calculation is as follows:
* <span class="swatch" style="--color: rgb(82.02% 30.21% 35.02%)"></span> rgb(82.02% 30.21% 35.02%) is lch(52% 58.1 22.7) which is X=0.3214, Y=0.2014, Z=0.0879.
* <span class="swatch" style="--color: rgb(5.64% 55.94% 85.31%)"></span> rgb(5.64% 55.94% 85.31%) is lch(56% 49.1 257.1) which is X=0.2070, Y=0.2391, Z=0.5249.
* mixed result X=(0.3214 * 0.7523) + (0.2070 * (1 - 0.7523)) = 0.29306.
* mixed result Y=(0.2014 * 0.7523) + (0.2391 * (1 - 0.7523)) = 0.21074.
* mixed result Z=(0.0879 * 0.7523) + (0.5249 * (1 - 0.7523)) = 0.19614.
* mix result is <span class="swatch" style="--color: rgb(72.300% 38.639% 53.557%)"></span> lch(53.0304% 38.9346 352.8138) which is rgb(72.300% 38.639% 53.557%)
</div>
<div class="example" id="ex-mix-blue-white">
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This example is a 50% mix of white and blue,
in three different color spaces.
<pre class="lang-css">
color-mix(in lch, white, blue);
color-mix(in oklch, white, blue);
color-mix(in srgb, white, blue);
</pre>
The calcuation is as follows:
* <span class="swatch" style="--color: white"></span> white
is rgb(100% 100% 100%)
which is lch(100% 0 none)
which is oklch(100% 0 none)
* <span class="swatch" style="--color: blue"></span> blue
is rgb(0% 0% 100%)
which is lch(29.5683% 131.201 301.364)
which is oklch(45.201% 0.31321 264.052)
* <span class="swatch" style="--color: rgb(68.594% 53.794% 100%)"></span> mix
in lch is lch(64.7841% 65.6008 301.364) which is quite purple
* <span class="swatch" style="--color: rgb(45.304% 63.808% 100%)"></span> mix
in oklch is oklch(72.601% 0.15661 264.052)
* <span class="swatch" style="--color: rgb(50% 50% 100%)"></span> mix
in srgb is rgb(50% 50% 100%) which is also a bit purple
</div>
<div class="example" id="ex-hsl-gamut-map">
This example is a mix of two colors,
in ''hsl'' color space,
where one of the colors to be mixed
is outside the ''sRGB'' gamut.
<pre class="lang-css">
color-mix(in hsl, color(display-p3 0 1 0) 80%, yellow);
</pre>
The calcuation is as follows:
* <span class="swatch oog" style="--color: white"></span> color(display-p3 0 1 0)
is color(srgb -0.5116 1.01827 -0.3107) which is outside the sRGB gamut
* Converted to ''hsl''
<span class="swatch oog" style="--color: rgb(0% 99.797% 0%)"></span>
hsl(127.879 301.946 25.334)
* <span class="swatch" style="--color: yellow"></span> yellow is
<span class="swatch" style="--color: yellow"></span> hsl(60 100% 50%)
* the hue is 127.879 × 0.8 + 60 × 0.2 = 114.3032
* the saturation is 301.946 × 0.8 + 100 × 0.2 = 261.5568
* the lightness is 25.334 × 0.8 + 50 × 0.2 = 30.2672
* the mixed result is
<span class="swatch oog" style="--color: rgb(72.66% 100% 0%)"></span> hsl(114.3032 261.5568 30.2672) which is
<span class="swatch oog" style="--color: rgb(72.66% 100% 0%)"></span> color(srgb -0.3387 1.0943 -0.48899)
</div>
<h3 id="color-mix-with-alpha">
Effect of Non-Unity Alpha on color-mix
</h3>
So far, all the ''color-mix()'' examples
have used fully opaque colors.
To simplify the examples,
the [=premultiplied|premultilication=] and unpremultiplication steps
were omitted
because these would simply multiply by 1, and divide by 1,
so the result would be unchanged.
In the general case,
colors may have non-unity alpha components
and thus the [=premultiplied|premultiply=], interpolate, unpremultiply steps
must not be omitted.
<div class="example" id="ex-premultiply-srgb">
This example is 25% semi-opaque red
and 75% semi-opaque green.
mixed in sRGB.
Both the correct ([=premultiplied=])
and incorrect (non-premultiplied)
workings are shown.
<pre class="lang-css">
color-mix(in srgb, rgb(100% 0% 0% / 0.7) 25%, rgb(0% 100% 0% / 0.2));
</pre>
The calcuation is as follows:
* <span class="swatch" style="--color: rgb(100% 0% 0% / 0.7)"></span> rgb(100% 0% 0% / 0.7)
when premultiplied, is [0.7, 0, 0]
* <span class="swatch" style="--color: rgb(0% 100% 0% / 0.2)"></span> rgb(0% 100% 0% / 0.2)
when premultiplied, is [0, 0.2, 0]
* the premultiplied, interpolated result is
[0.7 * 0.25 + 0 * (1 - 0.25), 0 * 0.25 + 0.2 * (1 - 0.25), 0 * 0.25 + 0 * (1 - 0.25)]
which is [0.175, 0.150, 0]
* the interpolated alpha is 0.7 * 0.25 + 0.2 * (1 - 0.25) = 0.325
* the un-premultiplied result is
[0.175 / 0.325, 0.150 / 0.325, 0 / 0.325]
which is [0.53846, 0.46154, 0]
* so the mixed color is
<span class="swatch" style="--color: rgba(53.846%, 46.154%, 0%, 0.325)"></span>
color(srgb 0.53846 0.46154 0 / 0.325)
The <em>incorrect</em> calculation would be:
* the interpolated result is
[1 * 0.25 + 0 * (1 - 0.25), 0 * 0.25 + 1 * (1 - 0.25), 0 * 0.25 + 0 * (1 - 0.25)]
which is [0.25, 0.75, 0]
* so the <em>incorrect</em> mixed color is
<span class="swatch" style="--color: rgba(25%, 75%, 0%, 0.325)"></span>
color(srgb 0.25 0.75 0 / 0.325)
This is a <em>huge</em> difference; the ΔE2000 between the correct and incorrect results is 30.7!
</div>
When the percentage normalization generates an alpha multiplier,
the calculation is the same except for an additional last step.
<div class="example" id="ex-premultiply-srgb-2">
This example is similar to the previous one,
25% semi-opaque red
and 75% semi-opaque green.
mixed in sRGB.
However in this case the percentages are specified as
20% of the first color and 60% of the second.
This adds to 80% so the alpha multiplier is 0.8.
The mix percentages are then scaled
by a factor of 100/80:<br>
20% * 100/80 = 25%<br>
60% * 100/80 = 75%<br>
giving the same final mix percentages as the previous example.
<pre class="lang-css">
color-mix(in srgb, rgb(100% 0% 0% / 0.7) 20%, rgb(0% 100% 0% / 0.2) 60%);
</pre>
The calcuation is as follows:
* <span class="swatch" style="--color: rgb(100% 0% 0% / 0.7)"></span> rgb(100% 0% 0% / 0.7)
when premultiplied, is [0.7, 0, 0]
* <span class="swatch" style="--color: rgb(0% 100% 0% / 0.2)"></span> rgb(0% 100% 0% / 0.2)
when premultiplied, is [0, 0.2, 0]
* the premultiplied, interpolated result is
[0.7 * 0.25 + 0 * (1 - 0.25), 0 * 0.25 + 0.2 * (1 - 0.25), 0 * 0.25 + 0 * (1 - 0.25)]
which is [0.175, 0.150, 0]
* the interpolated alpha is 0.7 * 0.25 + 0.2 * (1 - 0.25) = 0.325
* the un-premultiplied result is
[0.175 / 0.325, 0.150 / 0.325, 0 / 0.325]
which is [0.53846, 0.46154, 0]
* so the mixed color would be
<span class="swatch" style="--color: rgba(53.846%, 46.154%, 0%, 0.325)"></span>
color(srgb 0.53846 0.46154 0 / 0.325)
* there is a 0.8 alpha multiplier,
so the alpha of the mixed result is actually 0.325 * 0.8 = 0.260
so the mixed color is actually <span class="swatch" style="--color: rgba(53.846%, 46.154%, 0%, 0.260)"></span>
color(srgb 0.53846 0.46154 0 / 0.260)
</div>
Note: do not multiply the interpolated alpha by the alpha multiplier
and then use that to undo premultiplication.
That would be correct if the mix percentages were not scaled to sum to 100%,
but they are, so doing it this way would adjust the mixed color <em>twice</em>.
<!--
Let's move this example to the appropriate section when we have the new syntax for making these low-level adjustments
<div class="example">
This example produces the mixture of a deep green and a sky blue,
in ''lch()'' color space (the default),
with the lightness being 40% of the lightness of the green
(and thus, 60% of the lightness of the blue).
The chroma and hue of the green are used unchanged in the mixed result.
<pre class="lang-css">color-mix(rgb(0% 42.35% 33.33%) lightness 40%, rgb(41.2% 69.88% 96.64%));</pre>
The calculation is as follows:
* <span class="swatch" style="--color: rgb(0% 42.35% 33.33%)"></span> rgb(0% 42.35% 33.33%) is lch(40.083% 32.808 171.175)
* <span class="swatch" style="--color: rgb(41.2% 69.88% 96.64%)"></span> rgb(41.2% 69.88% 96.64%) is lch(70% 42.5 258.2)
* mixed lightness is 40.083 * 0.4 + 70% * (1 - 0.4) = 58.0332
* mixed result is <span class="swatch" style="--color: rgb(26.25% 60.68% 50.72%)"></span> lch(58.0332 32.808 171.175)
* which is a <span class="swatch" style="--color: rgb(26.25% 60.68% 50.72%)"></span> rgb(26.25% 60.68% 50.72%), a lighter green
</div>
<div class="example">
This example produces the mixture of a red and a sky blue,
in ''lch()'' color space (the default),
with the hue being 75.23% of that of the red
(and thus, 24.77% of that of the blue).
The shorter hue arc will be used.
The chroma and lightness of the red are left unchanged.
<pre class="lang-css">color-mix(lch(52% 58.1 22.7) hue 75.23%, lch(56% 49.1 257.1));</pre>
<figure id="fig-LCH-red-skyblue">
<img src="images/CH-mixing2.svg" style="width: 50vmin">
<figcaption>Mixtures of a red and a sky blue.
The red has a hue angle, measured from the positive a axis,
of 22.7 degrees
while the blue has a hue angle of 257.1 degrees.
The red has a chroma, or distance from the central neutral axis, of 58.1
and the chroma is not interpolated here, just the hue.
Thus, mixtures lie along the dashed circle.
</figcaption>
</figure>
The calculation is as follows:
* <span class="swatch" style="--color: rgb(82.02% 30.21% 35.02%)"></span> lch(52% 58.1 22.7)
* <span class="swatch" style="--color: rgb(5.64% 55.94% 85.31%)"></span> lch(56% 49.1 257.1)
* hue difference is |257.1 - 22.7| = 234.4, which is greater than 180; the shorter arc is 54.4 degrees.
* mixed hue is (22.7 + 360) * 0.7523 +(257.1 * 0.2477 = 351.59 degrees
* mixed result is <span class="swatch" style="--color: rgb(80.672% 28.822% 55.255%)"></span> lch(52% 58.1 351.59)
</div>
<div class="example">
This example produces the mixture of a red and a sky blue,
in ''lch()'' color space (the default),
with the hue being 75.23% of that of the red
(and thus, 24.77% of that of the blue).
The longer hue arc has been specified.
The chroma and lightness of the red are left unchanged.
<pre class="lang-css">color-mix(lch(52% 58.1 22.7) hue longer 75.23%, lch(56% 49.1 257.1) );</pre>
<figure id="fig-LCH-red-skyblue-2">
<img src="images/CH-mixing2b.svg" style="width: 50vmin">
<figcaption>Mixtures of a red and a sky blue.
The red has a hue angle, measured from the positive a axis,
of 22.7 degrees
while the blue has a hue angle of 257.1 degrees.
The red has a chroma, or distance from the central neutral axis, of 58.1
and the chroma is not interpolated here, just the hue.
Thus, mixtures lie along the dashed circle.
</figcaption>
</figure>
The calculation is as follows:
* <span class="swatch" style="--color: rgb(82.02% 30.21% 35.02%)"></span> lch(52% 58.1 22.7)
* <span class="swatch" style="--color: rgb(5.64% 55.94% 85.31%)"></span> lch(56% 49.1 257.1)
* hue difference is |257.1 - 22.7| = 234.4, which is greater than 180, but the long arc was requested.
* mixed hue is 22.7 * 0.7523 + 257.1 * 0.2477 = 80.76
* mixed result is <span class="swatch" style="--color: rgb(61.11% 45.85% 0.41%)"></span> lch(52% 58.1 80.76)
</div>
<div class="example">
This example produces the mixture of
the same two colors as the previous example
(a red and a sky blue),
in ''lch()'' color space (the default),
with the hue being 75.23% of that of the red
(and thus, 24.77% of that of the blue).
This time, the lightness is set to 68.4% and
the chroma is left unchanged.
<pre class="lang-css">color-mix(rgb(82.02% 30.21% 35.02%) hue 75.23% lightness 68.4%, rgb(5.64% 55.94% 85.31%) );</pre>
The calculation is as follows:
* <span class="swatch" style="--color: rgb(82.02% 30.21% 35.02%)"></span> rgb(82.02% 30.21% 35.02%) is lch(52% 58.1 22.7)
* <span class="swatch" style="--color: rgb(5.64% 55.94% 85.31%)"></span> rgb(5.64% 55.94% 85.31%) is lch(56% 49.1 257.1)
* mixed hue is 22.7 * 0.7523 + 257.1 * 0.2477 = 80.76
* new lightness is specified as 68.4%
* mixed result is <span class="swatch" style="--color: rgb(79.67% 62.48% 22.09%)"></span> lch(68.4% 58.1 80.76) which is rgb(79.67% 62.48% 22.09%)
</div>
<div class="example">
This example produces the mixture of red and yellow,
in ''lch()'' color space (the default),
with the lightness being 30% of the lightness of red
(and thus, 70% of the lightness of yellow).
The chroma and hue of red are left unchanged.
<pre class="lang-css">color-mix(red lightness 30%, yellow );</pre>
The calculation is as follows:
* sRGB <span class="swatch" style="--color: red"></span> red (#F00) is lch(54.2917% 106.8390 40.8526)
* sRGB <span class="swatch" style="--color: yellow"></span> yellow (#FF0) is lch(97.6071% 94.7077 99.5746)
* mixed lightness is 54.2917 * 0.3 + 97.6071 * 0.7 = 84.6125
* mixed result is <span class="swatch oog"></span> lch(84.6125% 106.8390 40.8526)
* which is a very light, saturated red
* (and well outside the gamut of sRGB: rgb(140.4967% 51.2654% 32.6891%))
* even outside the gamut of P3: color(display-p3 1.3033 0.5756 0.4003)
This example demonstrates that not all colors which can be mixed, can be displayed on current devices.
</div>
-->
<!--
<img src="images/mix_red_yellow_lightness30.png" alt="Result of color-mix(red, yellow, lightness(30%)" />
this image incorrectly shows red and yellow to be outside gamut as well, which is confusing.
it also shows the result color after per-component clipping, which is not desirable -->
<!--
<img src="images/mix_red_yellow_65.png" alt="Result of color-mix(red, yellow, 65%" /> -->
<!-- todo: example that specifies a different color space -->
<!-- worked example in Lab space
with 38% of a and 38% of b
showing desaturated result compared to LCH interpolation
red=[52, 58.1, 22.7]
Array(3) [ 52, 58.1, 22.7 ]
blue=[56, 49.1, 257.1]
Array(3) [ 56, 49.1, 257.1 ]
red_lab=LCH_to_Lab(red)
Array(3) [ 52, 53.59946299740792, 22.42114105904291 ]
blue_lab=LCH_to_Lab(blue)
Array(3) [ 56, -10.961580696137688, -47.860774634788996 ]
result_lab=[red_lab[0], 0.38*red_lab[1]+0.62*blue_lab[1], 0.38*red_lab[2]+0.62*blue_lab[2]]
Array(3) [ 52, 13.571615907409644, -21.153646671132876 ]
result_lch=Lab_to_LCH(result_lab)
Array(3) [ 52, 25.132956965414664, 302.683148992448 ]
result_rgb=LCH_to_sRGB(result_lch)
Array(3) [ 0.524461282381659, 0.4582102541032295, 0.6295269395052022 ]
which is rgb(52.446% 45.821% 62.953%)
<div class="example">
This example produces the mixture of
the same two colors as the previous example
(a red and a sky blue),
in Lab color space,
with 38% of a and 38% of b.
The lightness of the red is left unchanged.
This shows a desaturated result, compared to LCH interpolation,
because interpolation is in a straight line on the <em>a,b</em> plane
and can thus pass close to the central, neutral axis.
<pre class="lang-css">color-mix(lab rgb(82.02% 30.21% 35.02%) a 38% b 38%, rgb(5.64% 55.94% 85.31%));</pre>
<figure id="fig-Lab-red-skyblue">
<img src="images/CH-mixing2c.svg" style="width: 50vmin">
<figcaption>Mixtures of a red and a sky blue.
The red has a hue angle, measured from the positive a axis,
of 22.7 degrees
while the blue has a hue angle of 257.1 degrees.
Interpolation is on the a,b plane.
Thus, mixtures lie along the dashed line
and pass closer to the neutral axis.
</figcaption>
</figure>
The calculation is as follows:
* <span class="swatch" style="--color: rgb(82.02% 30.21% 35.02%)"></span> rgb(82.02% 30.21% 35.02%) is lab(52% 53.599 22.421)
* <span class="swatch" style="--color: rgb(5.64% 55.94% 85.31%)"></span> rgb(5.64% 55.94% 85.31%) is lab(56% -10.962 -47.861)
* a is (53.599 * 0.38) + (-10.962 * 0.62) = 13.572
* b is (22.421 * 0.38) + (-47.861 * 0.62) = -21.154
* result is <span class="swatch" style="--color: rgb(52.446% 45.821% 62.953%)"></span> lab(52% 13.572 -21.154) which is rgb(52.446% 45.821% 62.953%)
</div>
-->
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<h2 id="relative-colors">
Relative Colors
</h2>
<h3 id="rcs-intro">
Processing Model for Relative Colors
</h3>
In previous levels of this specification,
the color functions could only specify colors in an absolute manner,
by directly specifying all of the color components.
The new <dfn export>relative color</dfn> syntax
extends [=modern color syntax=]
to allow existing colors to be modified
using the color functions:
if an <dfn>origin color</dfn> is specified,
then each color component
(and the alpha component, if specified)
can <em>either</em> be directly specified,
or taken from the origin color
(and possibly modified with [=math functions=]).
The origin color and the relative color need not use the same color function.
<dfn export>Required conversion</dfn>:
All operations take part in the
[=color space=] of the [=relative color=] function;
if the
<dfn export>originally specified color space</dfn>
for the [=origin color=] used a different color function,
it's first converted into the chosen color function,
so it has meaningful values for the components,
and [=component keywords=]
refer to the color space of the relative color,
<em>not</em> the [=origin color=].
If the alpha value of the relative color is omitted,
it defaults to that of the [=origin color=]
(rather than defaulting to ''100%'', as it does in the absolute syntax).
When relative color syntax is used,
<strong>color component</strong> values,
whether directly specified
or arising from color space conversion,
are <em>not clamped</em> to the reference ranges but are retained as-is.
This preserves out of gamut values,
if the destination color space is capable of representing them.
However, when relative color syntax is used,
<strong>alpha component</strong> values
whether directly specified
or arising from color space conversion,
<em>are</em> clamped to the reference range.
Missing components are handled the same way as with
[[css-color-4#interpolation-missing]]:
the origin colorspace and the relative function colorspace
are checked for [=analogous components=]
which are then [=carried forward=] as missing.
While most uses of [=relative color=] syntax
will use the [=component keywords=] in their corresponding argument,
you can use them in any position.
Beware when using components outside their normal position;
when percentages are resolved to numbers,
there is no "magic scaling"
to account for the changed position
if those numbers are used in a different place.
<h3 id="relative-syntax">
Relative Color Syntax
</h3>
The precise details of each function's syntactic changes
to accommodate [=relative colors=] are listed below,
but they all follow a common structure:
* An [=origin color=] can be specified with a ''from <<color>>'' value
at the start of the function.
This includes the optional alpha component, if specified.
* If no origin color is specified, the function is not a relative color.
* If an [=origin color=] is specified,
the remaining arguments can either be specified directly, as normal,
or be specified as a <dfn>component keyword</dfn>
referring to one of the components of the [=origin color=]
converted to the [=color space=] of the relative color.
[=Math functions=] can also use these keywords
to do dynamic modifications of the [=origin color's=] components.
* [=Relative color=] syntax doesn't change whether an argument is required or optional.
* Relative color syntax only applies to the [=modern color syntax=].
It <em>cannot</em> be used with <a>legacy color syntax</a>
and attempting to do so is an error.
* However, the [=origin color=] can use either modern or legacy syntax.
The [=component keywords=] return a <<number>>, or ''none'';
if they were originally specified as a <<percentage>> or an <<angle>>,
that <<percentage>> is resolved to a <<number>>
and the <<angle>> is resolved to a <<number>> of degrees
(which is the [=canonical unit=])
in the range [0, 360].
<wpt>
relative-currentcolor-a98rgb-01.html
relative-currentcolor-lch-01.html
relative-currentcolor-rgb-01.html
relative-currentcolor-displayp3-01.html
relative-currentcolor-oklab-01.html
relative-currentcolor-rgb-02.html
relative-currentcolor-hsl-01.html
relative-currentcolor-oklch-01.html
relative-currentcolor-xyzd50-01.html
relative-currentcolor-hsl-02.html
relative-currentcolor-prophoto-01.html
relative-currentcolor-xyzd65-01.html
relative-currentcolor-hwb-01.html
relative-currentcolor-rec2020-01.html
relative-currentcolor-lab-01.html
relative-currentcolor-rec2020-02.html
relative-currentcolor-visited-getcomputedstyle.html
parsing/color-computed-relative-color.html
parsing/color-invalid-relative-color.html
parsing/color-valid-relative-color.html
parsing/relative-color-out-of-gamut.html
</wpt>
<div class=example>
For example, if a color is specified using <<percentage>>,
then RCS in the same colorspace will use the resolved <<number>> form:
<pre highlight=css>
html { --bluegreen: <span class="swatch" style="--color: teal"></span> oklab(54.3% -22.5% -5%); }
.overlay {
background: <span class="swatch" style="--color: rgb(4.696% 39.17% 39.38%)"></span> oklab(from var(--bluegreen) calc(1.0 - l) calc(a * 0.8) b);
}
</pre>
In this example, the specified percentages are resolved to numbers,
giving oklab(0.543 -0.09 -0.02).
The resulting RCS color has l = 1 - 0.543 = 0.457,
a = -0.09 * 0.8 = -0.072,
and b is unchanged at -0.02:
oklab(0.457 -0.072 -0.02).
</div>
<div class="example">
For example, if the origin color has a hue <<angle>> specified in degrees,
then RCS in the same colorspace will use the resolved <<number>> form:
<pre highlight=css>
html { --base: <span class="swatch" style="--color: sienna"></span> oklch(52.6% 0.115 44.6deg) }
.summary {
background: <span class="swatch" style="--color: rgb(30.09% 47.36% 18.46%)"></span> oklch(from var(--base) l c calc(h + 90));
}
</pre>
In this example the resulting RCS color is oklch(0.526 0.115 134.6).
Had the origin color hue <<angle>> been specified in another unit,
such as radians or turns,
still the resolved <<number>> would be the number of degrees.
</div>