I recently ran into this problem on a word press installation:
Everything in the admin pages was laid out correctly but all I was the borders of the positioned elements. It looked as if all the background colors/images where missing. Upon closer inspect in firebug, I noticed that colors-fresh.min.css was coming back as 404 file not found even though it was on the server:
To correct the problem I created an .htaccess file for the WordPress installation and then set the permalinks to post-name. This wrote to the .htaccess file. Which allowed the css file to resolve on the server and restore visual beauty to the WordPress admin panel.