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Excerpt from Color Vision and Colorimetry: Theory and Applications, Second Edition
Probably the first attempts to produce color curves describing the trichromatic theory of color were those by Maxwell (1857, 1860). As described earlier, the first chromaticity diagram was a circle devised by Newton. Later, Maxwell used an equilateral triangle (Fig. 3.1). In his trichromatic theory, each of the three primary colors—red, green, and blue—is located at a corner of the triangle. The white color is in the middle. Other colors are formed by a combination of the r, g, b components depending on the distances from each of the three sides of the triangle. This triangular representation has been used often with several modifications. It is not clear how Maxwell defined and used it.1