James Gurney has just published the best explanation of the properties of black that I have ever seen. He has done a four part examination of its use as a pigment, in composition, and properties as a color...or not. This last installment was my favorite. As it turns out, it depends on the context of the discussion, and its relation to other colors. This man is a heck of an educator!
If you don't read his blog yet, I highly recommend it. GurneyJourney.blogspot.com