[css-color] Missed a few color functions.

Author: tabatkins

css-color/Overview.bs

@@ -122,7 +122,8 @@ Representing Colors: the <<color>> type</h2>
 
 	<pre class='prod'>
 	<dfn>&lt;color></dfn> = <<rgb()>> | <<rgba()>> | <<hsl()>> | <<hsla()>> |
-	          <<hwb()>> | <<hex-color>> | <<named-color>> | currentcolor
+	          <<hwb()>> | <<gray()>> | <<device-cmyk()>> | <<color()>> |
+	          <<hex-color>> | <<named-color>> | currentcolor
 	</pre>
 
 	Some operations work differently on <dfn export>achromatic</dfn> colors.

css-color/Overview.html

@@ -261,7 +261,8 @@ <h2 class="heading settled heading" data-level=3 id=color-type><span class=secno
 <p>	In total, the definition of <a class="production css-code" data-link-type=type href=#typedef-color title="<color>">&lt;color&gt;</a> is:
 
 	<pre class=prod><dfn class=css-code data-dfn-type=type data-export="" id=typedef-color>&lt;color&gt;<a class=self-link href=#typedef-color></a></dfn> = <a class="production css-code" data-link-type=function href=#funcdef-rgb title=rgb()>&lt;rgb()&gt;</a> | <a class="production css-code" data-link-type=function href=#funcdef-rgba title=rgba()>&lt;rgba()&gt;</a> | <a class="production css-code" data-link-type=function href=#funcdef-hsl title=hsl()>&lt;hsl()&gt;</a> | <a class="production css-code" data-link-type=function href=#funcdef-hsla title=hsla()>&lt;hsla()&gt;</a> |
-          <a class="production css-code" data-link-type=function href=#funcdef-hwb title=hwb()>&lt;hwb()&gt;</a> | <a class="production css-code" data-link-type=type href=#typedef-hex-color title="<hex-color>">&lt;hex-color&gt;</a> | <a class="production css-code" data-link-type=type href=#typedef-named-color title="<named-color>">&lt;named-color&gt;</a> | currentcolor
+          <a class="production css-code" data-link-type=function href=#funcdef-hwb title=hwb()>&lt;hwb()&gt;</a> | <a class="production css-code" data-link-type=function href=#funcdef-gray title=gray()>&lt;gray()&gt;</a> | <a class="production css-code" data-link-type=function href=#funcdef-device-cmyk title=device-cmyk()>&lt;device-cmyk()&gt;</a> | <a class="production css-code" data-link-type=function href=#funcdef-color title=color()>&lt;color()&gt;</a> |
+          <a class="production css-code" data-link-type=type href=#typedef-hex-color title="<hex-color>">&lt;hex-color&gt;</a> | <a class="production css-code" data-link-type=type href=#typedef-named-color title="<named-color>">&lt;named-color&gt;</a> | currentcolor
 </pre>
 <p>	Some operations work differently on <dfn data-dfn-type=dfn data-export="" id=achromatic>achromatic<a class=self-link href=#achromatic></a></dfn> colors.
 	An <a data-link-type=dfn href=#achromatic title=achromatic>achromatic</a> color is a shade of gray: