Evaluation of the degree of fading on exposed paints by visual means alone obscures the underlying physical behavior of the pigments. It is shown that Mother Nature is logical and that, when hiding is complete, and the dispersion is uniform, the rate of fading is constant and is not appreciably affected by many of the variables of paint formulation, such as pigment volume concentration. On this basis, the observed visual changes are also predictable. When hiding is incomplete, however, the rate of fading increases and is dependent on the nature of the substrate. Illustrations of these phenomena are presented. 1985 Joseph J. Mattiello Memorial Lecture.