[css-color-adjust-1] Cross-ref css-color-4.

Author: fantasai

css-color-adjust-1/Overview.bs

@@ -391,7 +391,8 @@ Properties Affected by Forced Colors Mode {#forced-colors-properties}
 	by matching all channels other than alpha
 	to the appropriate forced background color;
 	which should be the corresponding system background color
-	if 'color' is a [=system color=],
+	if 'color' is a [=system color=]
+	(see [[!CSS-COLOR-4]]),
 	and ''Canvas'' otherwise.
 
 	Additionally, on <em>on user input controls (except button-like controls) only</em>: