[css-color-4] Split initial step of color interpolation into mandatory preparation and if-needed color space conversion, #10211

Author: svgeesus

css-color-4/Overview.bs

@@ -4797,10 +4797,11 @@ Color Interpolation</h2>
 	<ol>
 		<li>checking the two colors for [=analogous components=]
 			which will be <dfn export>carried forward</dfn></li>
-		<li>converting them to a given color space
+		<li>prepare both colors for conversion.
+			this changes any [=powerless=] components to [=missing=] values
+		</li>
+		<li>converting them both to a given color space
 			which will be referred to as the <dfn export>interpolation color space</dfn> below.
-			If one or both colors are already in the interpolation color space,
-			this conversion changes any [=powerless=] components to [=missing=] values
 		</li>
 		<li>(if required) re-inserting [=carried forward=] values in the converted colors</li>
 		<li>(if required) fixing up the hues, depending on the selected <<hue-interpolation-method>></li>