[xmonad] Border colors dependent on layout algorithm

[Jacob King]

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