Some recent empirical studies concerning the perception of tonal melodies are based upon the theoretical assumption that it is adequate to distinguish "tonal" from "atonal" tunes with reference to diatonic and chromatic pitch collections, respectively. Such a principal of demarcation, however, fails to account for the intuitive sense that melodies may display relative degrees of "tonal-ness" and that chromaticism may function to establish and reinforce tonal centers. What appears necessary for the evaluation of results of such studies, as well as for the formulation of further experiments, is a tonal-functional theory of chromaticism that will allow the distinction between "tonal" and "atonal" to be appropriately clarified. This article presents an informal model for a functional theory of chromaticism based upon a "tonal chromatic" scale. Drawing upon a critique of a functional model formulated by Deutsch and Feroe, this study develops concepts central to the notion of chromatic function. These concepts are then employed in a critique of four proposed forms of chromatic scales, specifying weaknesses in each. Following this, the author proposes a "tonal chromatic" scale which overcomes difficulties inherent in previously proposed scale forms. Analytical examples are offered that illuminate the structural implications of the model.