Primary Colors: Yellow, Red and Blue (YRB)

Secondary Colors: Orange Violet and Green (OVG)

Primary Hues

These are red, blue and yellow in the Prang color system. They are referred to as primary because (theoretically at least) they cannot be made by mixing other hues and because other hues can (again in theory) be made by mixing two of the primaries together.

Secondary Hues

These are orange, green and violet in the Prang system. These can each be produced by mixing together two primary hues.

Tertiary Hues

These are hues intermediary between primary and secondary hues. These are usually named and mixed by combining adjacent primary and secondary hues; e.g. red-orange is the tertiary between red and orange.

(Read more: http://www.uwgb.edu/heuerc/2d/colorsystm.html ; May 30, 2012)