Open folders ->blogs -> skins_adm ->login->_login_form.main.php

Thank you John.

Open folders ->blogs -> skins_adm ->login->_login_form.main.php

I looked at the file and couldn't find where I can change the background color for example.

Any help would be appriciated.

You'll need to look at the CSS file for whichever admin skin you're using. They seem to be in the rsc folder for the skins

I found it and it worked out just fine,
Thanks Chris