[css-color-4] tidy untagged section

Author: svgeesus

css-color-4/Overview.bs

@@ -143,7 +143,7 @@ Accessibility and Conveying Information By Color</h3>
 	> Color is not used as the only visual means of conveying information,
 	> indicating an action, prompting a response, or distinguishing a visual element</a>
 
-<h3 id='sRGB'>
+<h3 id='untagged'>
 Color Spaces of Untagged Colors</h3>
 
 	Colors specified in HTML and [=untagged images=] are in the sRGB color space ([[!SRGB]])
@@ -156,8 +156,6 @@ Color Spaces of Untagged Colors</h3>
 	* At 720p, it is SMPTE ST 296 (same colorimetry as 709) [[!SMPTE296]]
 	* At 1080p, it is Recommendation ITU-R BT.709 [[!ITU-R-BT.709]]
 
-	Issue(287): What is the colorspace for <{video}>?
-
 <h3 id='resolving-color-values'>
 Resolving <<color>> Values</h3>