[css-color-4] Exclude none as a component name

css-color-4/Overview.bs

@@ -4330,6 +4330,12 @@ Specifying a color profile: the ''@color-profile'' at-rule</h3>
 	in the order in which they are used in the color profile,
 	while the total number of tokens defines the number of components.
 
+	A component must not be named none,
+	because that would clash with the token for missing values.
+	If this descriptor contains a component called none,
+	the descriptor is invalid.
+
+
 	<div class="example" id="ex-components-cmyk">
 		This descriptor declares that there are four components named cyan, magenta, yellow and black:
 		<pre>components: cyan, magenta, yellow, black</pre>