[css-color-adjust] Per WG resolution, respect chosen system colors when force-adjusting. w3c#4178

tabatkins · tabatkins · commit 7c154ddc7f19 · 2020-08-19T15:43:31.000-07:00
diff --git a/css-color-adjust-1/Overview.bs b/css-color-adjust-1/Overview.bs
@@ -359,14 +359,11 @@ Forced Color Schemes: the 'forced-color-adjust' property {#forced}
 Properties Affected by Forced Colors Mode {#forced-colors-properties}
 -----------------------------------------
 
-	When  <a>forced colors mode</a> is active
-	and 'forced-color-adjust' is ''forced-color-adjust/auto'' (see below),
-	colors must be force-adjusted to the user’s preferred color palette.
+	When <a>forced colors mode</a> is active
+	and 'forced-color-adjust' is ''forced-color-adjust/auto'' (see below) on an element,
+	colors on the element must be force-adjusted to the user’s preferred color palette.
 
-	Any [=author origin=] or [=animation origin=] declaration
-	of the following properties on any element
-	(including any declarations representing a non-CSS presentational hint)
-	is rewritten to specify ''revert'':
+	For each of the following properties:
 
 	<ul>
 		<li>'color'
@@ -383,29 +380,32 @@ Properties Affected by Forced Colors Mode {#forced-colors-properties}
 		<li>'text-shadow'
 	</pre>
 
-	Additionally, 'background-image', unless the value is a 'url()' function.
+	if the [=computed value=] would be a color other than a [=system color=],
+	it must instead compute to an appropriate [=system color=],
+	as chosen by the user agent.
+
+	For this purpose, any color value with the capability of "fallback" to another color,
+	such as the ''color()'' function,
+	must be allowed to fall back to a system color if specified.
+
+	The "appropriate system color" for 'background-color'
+	must be matched to 'color':
+	if 'color' is a [=system color=],
+	'background-color' must be the opposite color
+	from the [=system color pairings=]
+	(taking ''canvastext'' if 'color' is ''canvas'',
+	and ''canvas'' if 'color' is ''graytext'').
+	It must also take its alpha channel from the original 'background-color' [=computed value=].
+
+	Additionally, 'background-image' is reset to ''none'' unless the original value is a 'url()' function.
 
 	'color-scheme' on the element must compute to ''light dark'',
 	to allow the user preference (see [[#forced|above]])
 	to be respected.
 
-	Based on the resulting [=computed value|computed=] 'color' value,
-	the [computed|used] 'background-color' of an element is forced
-	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=]
-	(see [[!CSS-COLOR-4]]),
-	and ''Canvas'' otherwise.
-
-	UA may further tweak these <a>forced colors mode</a> heuristics
+	UAs may further tweak these <a>forced colors mode</a> heuristics
 	to provide better user experience.
 
-	Note: See [[CSS-CASCADE-4]] for information about
-	[=cascade origins=],
-	[[css-cascade-4#preshint|non-CSS presentational hints]],
-	and the ''revert'' keyword.
-
 Opting Out of a Forced Color Scheme: the 'forced-color-adjust' property {#forced-color-adjust-prop}
 -----------------------------------------------------------------
 
