[css-color-5] [[editorial] Add WPT for RCS with currentColor, w3c#7978

Author: svgeesus

css-color-5/Overview.bs

@@ -2331,6 +2331,10 @@ or any other color or monochrome output device which has been characterized.
 		with each <<color>> parameter resolved according to [[css-color-4#resolving-color-values]],
 		thus preserving inheritance into child elements.
 
+		<wpt>
+			nested-color-mix-with-currentcolor.html
+		</wpt>
+
 <h3 id="resolving-device-cmyk-values">
 	Resolving ''device-cmyk'' Values
 </h3>