Hexachrome color theory

MacEVOY Bruce (2005). Watercolors. The world's finest guide to watercolor painting. Retrievable from Handprint.com, 2010.

Somewhere in this website there is a good introduction to the "hexachrome" theory to color mixing (try the "chapter" Color wheels for an exposition of the theory, and the "chapter" An artist's color wheel for an introduction to mixing using the hexachrome theory). The author uses watercolors as his main referent, but the theory is equally applicable to other painting media.