David Briggs' The Dimensions of Colour, a comprehensive online explanation of traditional (what you've probably been taught) and modern colour theory, and its applications to visual art. Invaluable for artists and non-artists alike. (The answer: probably some kind of brown. Yes, your kindergarten teachers fed you lies.)
Four years ago, we showed English language speakers random colors and asked for the color names. Four years later, with CrowdFlower contributors now in every country of the world, the experiment becomes much richer.
Friday Flash Fun: Color Theory is a puzzle platformer about... um... color theory. And gravity switching. And aliens. Via the eternal font of pleasant time-wasters, jayisgames.
The Virtual Colour Museum presents Colour Order Systems in Art and Science: "a complete cultural history of colour", including illustrated explanations of 59 colour theories from antiquity to modern time, plus the significance of colours in various cultural systems (click the small images to enlarge), and a "virtual colour-space" dedicated to illustrating the spherical colour system construction of early 19th century painter Philipp Otto Runge. Walk this way >>