THings such as tone and contrast, dominance and subordination, etc.
Color, Structure, and Design, Richard G. Ellinger, is a good place to start, it's old but solid, 137 pages. :-) To really get the gist you actually have to do the exercises, but it's a quick read and a solid color theory reference.
edit: LOL . . . seeing copies starting at .01 on Amazon . . .