I ran across ColorBrewer2.org a few days ago. This looks to be a tremendously useful tool for cartographers. It lets you see how distinguishable different colors are on a map.
When I’m making maps it often happens that I use two colors that are too much alike for two completely different data classes. Unfortunately I usually don’t spot that right away so I end up having to remake a number of maps. Hopefully this tool can help me avoid some of those mistakes.
(found via Axis Maps Blog)