I'm sure this has probably been suggested already, but it would be nice to have a window in both ZQuest and ZC to allow us to create our own custom GUI color schemes. Basically, you'd have something similar to the palette editor, but with maybe 3 cSets for custom schemes. They would be saved in the ag.cfg file, and like other palette windows, there would of course be an option for grabbing from a picture. Each scheme would be assigned its own gui_colorset value, as well as a name to identify it for the next suggestion. My other suggestion would be to have an option that allows you to select from the available schemes right inside ZC and ZQ, so you don't have to manually edit the config each time you want to change the scheme.
Custom GUI Colorsets
Wow, I always wanted more gui_colorsets, there are just a few now, a gui_colorset editor could be great, perhaps it could export the colorset to a .pal file or something like that, so "skins" could be traded.