[css-fonts-4] Add clarifying note, fix #6916

Author: svgeesus

css-fonts-4/Overview.bs

@@ -7160,8 +7160,16 @@ User-defined font color palettes: The ''@font-palette-values'' rule</h3>
 
 	The <dfn>@font-palette-values</dfn> rule defines a color palette
 	and associates that color palette with a specific font.
-	This allows a web author to select arbitrary colors to use inside a color font
+	This allows a web author to select arbitrary <<color>>s to use inside a color font
 	rather than being limited to the preexisting palettes inside font files.
+
+	Note: The OpenType 'CPAL' table is restricted to sRGB colors.
+	The <<color>>s in ''@font-palette-values'' allow any CSS color.
+	Some implementations currently use APIs which are restricted to sRGB
+	and may therefore map the specified colors to sRGB.
+	This is expected to be a temporary limitation.
+	Authors should not rely on this mapping to sRGB.
+
 	In addition, this rule's association with a specific font
 	allows a name of a palette to apply differently to different fonts,
 	which allows similar colors to be used across multiple fonts