re: Not to go off on a tangent, but...
When I was studying art in college/visual arts, my painting professor, I had a separerate one for drawing and another one for sculpture, anyways, he taught us never to use the color Black when painting, instead to mix Naphtol Crimson Red, Ultramarine Blue and a dark brown (a mix of a dark green and red, will give you brown) and that would give you close to a 'true' black. Even coal will reflect different colors depending on the light. He said that a true black was not always found in nature.
As for white, it is always used to highlight, but always mixed with another color.
Of course, anything goes in abstract art.