[css-color-5] issue w3c#4747

Author: svgeesus

css-color-5/Overview.bs

@@ -79,6 +79,8 @@ Mixing colors: the ''color-mix'' function {#colormix}
 		[ <<color-function>> <<colorspace>>? ]?] )
 </pre>
 
+Issue(4747): <a href="https://github.com/w3c/csswg-drafts/issues/4747">color-function used but not defined</a>
+
 <div class="example">
 	This example produces a mixture of 40% <span class="swatch" style="--color: peru"></span> peru
 	and 60% <span class="swatch" style="--color: lightgoldenrod"></span> lightgoldenrod.