Aesthetics Online: Website of the American Society for Aesthetics.
Color Wheels, Charts, and Tables Through History. From the Public Domain Review.
Electronic Swatchbook. From the Powerhouse Museum. Thousands of fabric swatches to search, including by color.
Goethe's Theory of Colors. Full text of 1840 available on the Internet Archive.
Plenty of Colour. "Inspiration devoted to colour." Great site with gorgeous photos of color in all its manifestations.
Walter Benjamin's Philosophical Thought Presented by Two Experimental Films. Watch films for free on Open Culture site.