A few tweaks to jQuery UI colours

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5336 2fea6a4d-a838-0410-917b-93a53c48e9d2
Remove unused #999999 ui-icon-sprite, add a #ffffff version

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5337 2fea6a4d-a838-0410-917b-93a53c48e9d2