About screen: Only show the pick-a-color section if there are 2 or more of the eight new color schemes available. And only show the eight core schemes.

This hides the section in develop.svn /src's directory (use /build for colors) and when a plugin is manipulating/unregistering colors. In both situations, which are rare, losing the section is fine.

This removes a fallback image as we were previously showing the section in these cases; the rest of the page shows off the design (and color opportunities) well enough on its own to avoid this confusing section.

see #26387.

Built from https://develop.svn.wordpress.org/trunk@26795


git-svn-id: http://core.svn.wordpress.org/trunk@26682 1a063a9b-81f0-0310-95a4-ce76da25c4cd