3.8 branch: Undo the colors.css changes in [26938] and move the rules to wp-admin.css.

This will prevent us from shipping a full re-build of the color schemes in 3.8.1.

see #26699.


git-svn-id: https://develop.svn.wordpress.org/branches/3.8@27023 602fd350-edb4-49c9-b593-d223f7449a82