[css-color-adjust-1] Add a quick line explaining 'normal' a bit more. w3c#5897

Author: tabatkins

css-color-adjust-1/Overview.bs

@@ -161,6 +161,8 @@ Opting Into a Preferred Color Scheme: the 'color-scheme' property {#color-scheme
 			Indicates that the element isn't aware of [=color schemes=] at all,
 			and so the element should be rendered with the browser's default [=color scheme=].
 
+			(This is typically, tho not always, similar to ''light''.)
+
 		: <dfn>light</dfn>
 		::
 			Indicates that the page can handle the element being rendered