AbstractIn phenomenological analyses of the visual color gestalt it has been found that color plays at least a double role from a cognitive point of view. First, the characteristics of the color gestalt have to do with how man identifies colors, and are related to emotions, connotations, semantics, and symbolism. The NCS (Natural Color System) was designed to cover the need for a descriptive color order system, based on the six characteristic elementary color attributes whiteness, blackness, yellowness, redness, blueness, and greenness, from which was derived the three‐dimensional NCS color space for providing color notations. Second, the form of background and patterns in a color gestalt has to do with how man distinguishes color elements from each other by contrast and is informative about form and directions. In this article we report about one of the contrast phenomena, border distinctness between adjacent colors, which is most essential for the perception of form gestalts. Several years of phenomenological analyses and psychometric and psychophysical experiments have resulted in an equation for the prediction of the kind of contrast defined as border distinctness, called GT from the Swedish word Gränstydlighet. Based on that equation is a geometrical model for the GT color‐difference space that is not Euclidean but of city‐block type. The studies have led to the question of whether the phenomenon of color contrast (difference) is a perception of its own and not linearly related to the difference between two color perceptions.