[stuntmouse]

now if i could just figure out a way to change the background color of the active window, i'd be all set. nice job.

[jrockway]

Surprisingly, it's M-x set-background-color. You can also change the background color of the default face; same thing.

[stuntmouse]

I should have been more specific. I'd like to change the background color of the active window to indicate which one has focus.

Your solution changes the background color for all windows.