[css-values-4] Color type not additive, fix #8576

Author: svgeesus

css-values-4/Overview.bs

@@ -2747,10 +2747,12 @@ Combination of <<color>></h4>
 	as defined in
 	[[css-color-4#interpolation-alpha]].
 
-	<a>Addition</a> of <<color>> is likewise defined as
-	the independent <a>addition</a> of each component
-	as a <<number>>
-	in premultiplied space.
+	The <<color>> type is <a>not additive</a>.
+
+	Note: the CSS WG is interested to 
+	<a href="https://github.com/w3c/csswg-drafts/issues/new">hear</a>
+	use-cases for addition of <<color>>,
+	and may consider making <<color>> additive in the future.
 
 
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