The Color Usage Research Lab is sponsored by NASA and has a very informative website. They focus on… wait for it… color usage. A lot of information on how to choose colors and present them well in charts and graphs and such. Some of this might not be useful to a web developer, however they do have a section on Color Science which is amazingly useful and quite interesting.
Color science covers lots of stuff such as color perception, how the eye works, why certain colors don’t go together, color and legibility and so on.
So if you’ve got a couple hours to kill I highly suggest you check out color science.