[xmonad] Border colors dependent on layout algorithm

In the spirit of making all state explicit, I want to hack up Xmonad to use different border colors depending on the mode. The particular situation of annoyance is when in full-screen mode, I forget that there are other hidden windows, and just assume that I'm in some other mode with only one window. There are a large number of configurations in which the current mode is not immediately discernable from the layout. Has anyone made such a modification? My first glance at the codebase suggests this is a nontrivial modification, and I didn't see anything related in the archives, so I figured it would be best to ask the mailing list before groking & hacking the project. Thanks, Jacob