[css-2020] Add css-color-4 per WG resolution. w3c#4715

Author: fantasai

css-2020/Overview.bs

@@ -309,6 +309,12 @@ Fairly Stable Modules with limited implementation experience</h3>
 			expanding the syntax, deprecating most media types,
 			and introducing new media features.
 
+		<dt><a href="https://www.w3.org/TR/css-color-4/">CSS Color Level 4</a>
+		  [[!CSS-COLOR-4]]
+		<dd>
+			Extends and supersedes [[CSS-COLOR-3]],
+			further expanding the range of colors expressable in CSS.
+
 		<dt><a href="https://www.w3.org/TR/css-display-3/">CSS Display Module Level 3</a>
 		  [[CSS-DISPLAY-3]]
 		<dd>