For opaque coloration systems, Kubelka-Munk turbid media theory is used commonly to model optical mixing behavior. Most educational publications on the subject use opaque paint systems when describing the two-constant approach and textile systems when describing the single-constant simplification. Because of the differences in defining concentration for these systems and the corresponding degrees of freedom, the single-constant simplification for paint and textile systems are not identical. The second edition of '' Principles of Color Technology '' showed a numerical example for all opaque paint system modeled using the textile equations. The third edition used the sanie example but modified the degrees of freedom, a hybrid of the paint and textile approaches. Recent research by Berns and Mohammadi has evaluated the single-constant simplification for modeling artist paints; they have,e used both the hybrid and paint approaches. Thus, it was oof interest to review these different approaches and determine whether these differences have practical importance and whether future printings and editions of Principles of Color Technology should be modified. The three approaches were tested for tints made from a mixture of cobalt blue and titanium white acrylic emulsion artist paints. The differences between the textile and hybrid approaches were inconsequential. The paint approach was superior and its use is recommend for opaque paint systems. The differences in the numerical example from Principles of Color Technology were very small. For future printings of the third edition, the example will remain unchanged. For future editions, including the numerical example remains all open question. (c) 2007 Wiley Periodicals, Inc.