mat-slide-toggle styling inconsistent

[arciisine]

Bug, feature request, or proposal:

As of #12698, changes were made to slide toggle styling to support the theme properly.

The issue is, that in the dark theme, the slide toggle styling relies on a key of 200 to be in the palette for coloring.
https://angular-kh6bg8.stackblitz.io

As far as I can tell, this is the only location that makes this choice. Everywhere else is dependent upon default, lighter, or darker.

What is the expected behavior?

That the slide toggle would rely upon default/lighter/darker for the checked state, in the dark theme.

What is the current behavior?

The slide toggle relies upon the palette's 200 value for the checked state in the dark theme.

Below is the current input I have to construct for mat-pallete to allow sass to compile

$mat-primary: (
  main: #cc33ca,
  lighter: #f0c2ef,
  darker: #b920b7,
  200: #cc33ca, // For slide toggle,
  contrast : (
    main: $light-primary-text,
    lighter: $dark-primary-text,
    darker: $light-primary-text,
  )
);
$theme-primary: mat-palette($mat-primary, main, lighter, darker);

$theme: mat-dark-theme($theme-primary, ... );

What are the steps to reproduce?

https://angular-kh6bg8.stackblitz.io

What is the use-case or motivation for changing an existing behavior?

That by default, when defining a theme, the only colors that are needed are lighter, darker, and default. There should not a need to define all the other colors in a custom theme.

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Material, latest

Is there anything else we should know?

[crisbeto]

@arciisine your Stackblitz link doesn't seem to load.

[arciisine]

Sorry about that, I forgot to fork before making changes, description has been updated with new links.

[arciisine]

Attaching an image as the stackblitz link seems to be slow to load.

[devversion]

I'm thinking about this, but somehow don't feel comfortable changing the dark hue to default. This is because:

• The new specs don't cover switches in dark mode at all
• The old specs explicitly stated that the hue 200 should be used in dark themes
• Using the default hue causes a bad contrast between the bar and thumb.

Following old specs	Using default hue

Note that MDC also seems to use the default (500) hue in dark mode. Though this does not necessarily mean that it's the intended color for dark themes.

[arciisine]

I added this to the description, but basically this toggle is unique in it's behavior. I am only adding provisions for the slide-toggle, and nothing else.

$mat-primary: (
  main: #cc33ca,
  lighter: #f0c2ef,
  darker: #b920b7,
  200: #cc33ca, // For slide toggle,
  contrast : (
    main: $light-primary-text,
    lighter: $dark-primary-text,
    darker: $light-primary-text,
  )
);
$theme-primary: mat-palette($mat-primary, main, lighter, darker);

$theme: mat-dark-theme($theme-primary, ... );

[devversion]

I see the issue about having to define the 200 hue just for the slide-toggle, but I think, usually a custom theme should include updated colors for all hues.

Even though developer experience is an important point, following the specs is also an important part. I'll try to collect more information, but I'm tending to just follow what MDC does (removing the hue 200)

[arciisine]

Looking at https://material.io/tools/color/#!/, and https://material.io/tools/theme-editor/, it looks like majority of the tools have knowledge of all the colors in the default Material palettes, but only require 3 colors per palette. Is this a fair assumption that the material angular project will follow that as well?

I'm currently working on a theme editor (http://materialtheme.arcsine.org) and I'm trying to align first with Material's theming, and then secondarily fit in with the angular implementation.

[devversion]

True, some implementations like MDC apparently just expect a single color for primary, secondary. This is different from our implementation because we expect primary and secondary to be a full palette of colors.

Quote from the specs

These palettes provide additional ways to use your primary and secondary colors, by providing lighter and darker options to separate surfaces and provide colors that meet accessibility standards.

I think we are good to change this away from 200 to default in the future, but since this is a breaking change, it won't be anytime soon.

The Material Design specifications also provide a tool to generate all hues based on a picked color. See https://material.io/design/color/the-color-system.html#tools-for-picking-colors

[arciisine]

And I have seen these tools, the issue for me is that knowing what 100-A700 mean within angular material can be challenging. I'm attempting to make it simpler for people who are not using the standard color palettes, as defining all those colors, and knowing how they will be used is not clear (apart from the default, lighter and darker).

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