[css-images-4] Make colors serialize correctly #7728

Author: svgeesus

css-images-4/Overview.bs

@@ -2426,7 +2426,7 @@ Serialization {#serialization}
 
 		must serialize as:
 
-		<pre>linear-gradient(red, yellow, black 100px)</pre>
+		<pre>linear-gradient(rgb(255, 0, 0), rgb(255, 255, 0), rgb(0, 0, 0) 100px)</pre>
 	</div>
 
 <h2 id=deprecated class=no-num>