The Dimensions of Color by David Briggs is an excellent (and easy-to-read) online resource for all things color. Highly recommend!
The Dimensions of Color by David Briggs:
“[The] website presents an account of the dimensions of colour and light perception, written for painters using either traditional or digital media. The conceptual framework presented here was developed as a component of Colour, Light and Vision, a course in colour theory and practice for artists that I have been presenting since 1998 at the Julian Ashton Art School, Sydney, of Theories of Colour, a lecture course on the history of colour theory and practice that I presented at the National Art School, Sydney, in 2009-2011, and of ongoing practical painting classes at both schools.”