Lynda.com - Hexidecimal color codes and RGB values for web safe colors.
http://www.lynda.com/hexh.html

Mundi Design Studios -Interactive guide to color relationships.
http://www.mundidesign.com/webct/

Adobe Technical Guides - In depth exploration of color theory.
http://www.adobe.com/support/techguides/color/colortheory/main.html

The Art Institute of California - San Francisco - How-to for choosing web colors.
http://www.aisf.artinstitutes.edu/news_pressReleasesDetail.asp?nid=192

Color Cube.com - Historic exhibit of color models and diagrams.
http://www.colorcube.com/articles/models/model.htm

Charles Poyton's Inforamp - Full of FAQs about colors and web publishing including reference materials - an invaluable resource.
http://www.inforamp.net/~poynton/notes/colour_and_gamma/ColorFAQ.html

Hype's Color Specifier -Hexidecimal codes for web colors that expand options far beyond the traditional web-safe palettes.
http://users.rcn.com/giant.interport/COLOR/1ColorSpecifier.htm

Birren, Faber (1969) "Munsell-A Grammar of Color", New York, Van Nostrand Reinhold Company

Cohen, Bernard I. and Westfall, Richard S. (1995) "Newton", New York and London, W.W.Norton & Co.

Gerritsen, Frans (1983) "Theory and Practice of Color", New York, Van Nostrand Reinhold Company

Gjertsen, Derek (1986) "The Newton Handbook", London and New York, Routledge & Kegan Paul

Hedgecoe, John (1989) "The Art of Color Photography" New York and London, Simon & Schuster Inc.

Itten, Johannes (1970) "The Elements of Color", New York, Van Nostrand Reinhold Company

Itten, Johannes (1973) "The Art of Color" , New York, Van Nostrand Reinhold Company

Jute, Andre (1993) "Colour for Professional Communicators" London, Batsford Ltd.

Korn, Jerry (1970) "Color" New York, Time-Life Books

Matthaei, Rupprecht (1970) "Goethe's Color Theory", New York, Van Nostrand Reinhold Company

McCanna, Laurie (1996) "Creating Great Web Graphics" MIS Press