Ultimate Branding – WordPress Login Branding

Hi There, I am in the process of configuring my WordPress multi-site network and really love the Ultimate Branding plugin. I like having the ability to remove the WordPress logo from the login page, however I was wondering if there was a way to modify the background colour of the login page. Is there a specific class I should be targeting? Can this be done without effecting or being overwritten by future WordPress upgrades? Can the plugin be modified to include this option?

Any help you can provide is greatly appreciated.