[css-color-4] Remove the paragraph about canvas surface, now that Backgrounds defines it well. Also remove the 'transparent' requirement; that's the initial value of 'background' anyway. w3c#4863

Author: tabatkins

css-color-4/Overview.bs

@@ -3072,12 +3072,6 @@ Default Style Rules</h2>
 	}
 	</pre>
 
-	The default background of the root element must be ''transparent''.
-	The default color of the canvas (the surface on which the document is painted)
-	is UA-dependent,
-	but is recommended to be ''white'',
-	especially if the above 'color' rules are used.
-
 
 <h2 id="color-conversion-code">Sample code for color conversions</h2>