Colors rarely appear alone, they usually appear together. Since the number of colors is very large, the number of color combinations is almost infinite. Consequently: it is difficult to investigate how people perceive and Evaluate color constellations in various contexts. It seems pointless to study arbitrarily chosen combinations. To bring order into the large number of possible color combinations, a structure is needed. The following article presents such a theoretical model-a theory, of colors in combination. The article is based on the Natural Color System for the ordering of singular colors, which is in turn the practical extension? of Hering's phenomenologically based Opponent Color Theory. Thus, the model is descriptive, i.e., the variables carry immediate meaning regarding the actual color appearance. Since the model is purely descriptive, it contains no information pei se of whether colors are beautiful together or not. However, the model can be used as a reference structure to investigate the attributes and connotations of the experience of a given color combination (some examples of this are given). The most relevant attributes, or dimensions, of color combinations al-e categorized into three main groups, each with three subfactors: The Color Interval, with the subvariables Distinctness of Border; Interval Kind and Interval Size, is the perceptual phenomenon that occurs in the transition from one color percept to another. The Color Chord, with subvariables Complexity: Chord Category, and Chord Type, expresses the character of the combination, how the colors "sound" together i.e., the totality of rite Color Gestalt. The Color Tuning, with subvariables Surface Relations, Color Relations, and Order Rhythm, refers to some of the different ways color combinations can be varied. The present color combination model should be seen as a theoretical, albeit empirically based starting point for further studies of people's perception of color constellations, a scientific area that still, probably because of its complexity, seems to be uncharted territory. (C) 2001 John Wiley & Sons, Inc.