[css-color-5] Tidy up and export "originally specified color space"

Author: svgeesus

css-color-5/Overview.bs

@@ -33,6 +33,7 @@ spec:css-color-4; type:value; text:none
 spec:css-color-4; type:value; text:srgb
 spec:css-color-4; type:dfn; text:modern color syntax
 spec:css-color-4; type:value; text:alpha-value
+spec:css-values-5; type:value; text:color
 </pre>
 <link rel="stylesheet" href="style.css" />
 <style>
@@ -887,7 +888,9 @@ in the range [0, 360].
 
 </div>
 
-<p id="required-conversion">If the [=origin color=] was <dfn>originally specified</dfn> with a different color function,
+<p id="required-conversion">If the 
+<dfn export>originally specified color space</dfn> 
+for the [=origin color=] used a different color function,
 it's first converted into the chosen color function,
 so it has meaningful values for the channels.</p>