There are a few different style sheets for the backoffice because it supports style switching (see the "V-D-L" in the upper right of the backoffice). Look in the admin folder for two style sheets:

variation.css
desert.css

Add this at the bottom of both of them and the background color should be changed:

body {
background: #999;
}

thanks a bunch, when i return from work ill give that a go....i was playing around with that style switching...doesnt seem to do a whole lot...

Hey there...those style sheets dont appear in my admin folder...anywhere else is should be looking?

nevermind...found them, thanks