accept more than one `wp_admin_css_color()`; refactored color scheme component; slightly adjusted MP6 preview colors; removed login styles from blue color scheme; removed filter that adds default admin color schemes, instead of unsetting them



git-svn-id: https://plugins.svn.wordpress.org/mp6/trunk@752185 b8457f37-d9ea-0310-8a92-e5e31aec5664