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Well styled.com: Webdesigner Tools: Color Scheme Generator
A totally cool concept! Choose your base color, your scheme (monochromatic, etc.) and the computer will show you what other colors go with it! There are even settings for various levels of color-blindness. A really cool art tool!!
ArtLex
Art Lex: Color
An in-depth instructional page on color that defines a variety of terms related to color.