[css-color-4][editorial] inadvertent normative reference to images-4 made informative

Author: Chris Lilley

css-color-4/Overview.bs

@@ -4349,7 +4349,7 @@ Color Space for Interpolation</h3>
 	These features are collectively termed the <dfn export>host syntax</dfn>.
 	They are not used by this specification itself, 
 	only exposed so that other specifications can use them; 
-	see e.g. use in [[css-images-4#linear-gradients]].
+	<span class="non-normative">see e.g. use in [[css-images-4#linear-gradients]].</span>
 	The host syntax should define
 	what the default [=interpolation color space=]  should be for each case,
 	and optionally provide syntax for authors to override this default.