Do you need that second color?

When money is short, two-color printing is often the first thing to go from technical manuals and instructional texts. Does their effectiveness suffer as a result? Conversely, when a second color is used, is it often just a waste of money? This paper sets out, first, the main purpose for which a second color can be used; second, technical and perceptual constraints on the use of color; and, third, research findings on color and learning. The purpose of the paper is to provide practical guidelines for decisions about the use of a second color in texts.