A few more links to online resources to help with choosing colors for maps and related graphics:
Color.org – Upload your own graphic image, then select colors from it by moving your cursor over the graphic and clicking on a color block. Add colors to a color scheme, or find complementary colors. Interface is a bit confusing, though, and there’s no help file.
ColorSchemer – Click on a single color, or enter the RGB/Hex value, and get a set of 16 complementary colors.
Whatsitscolor – “Whats its color is an image-color processing utility that will evaluate an image and give you the image’s primary and complementary dominant colors of an image, how many visually unique colors are in an image, and the top ten visually unique colors in an image. Extremely useful when creating any type of designs around an image. The more colorful the image, the better the results. Results will display your image on the best suited background for that image.”