..is there an easy way to do it? I'm not talking about the background of the composition itself, but the window. I'm working on a job with various shades of grey backgrounds, most of which are exactly the same as the comp window background shades available by changing the display brightness in the preferences. So it's hard to see the edge of the comp.
I wondered if there's a way like shift-paint-bucket-clicking the background like you can in Photoshop (well, there's a preference menu for it in CS5 - they've taken all the mystery away!).