Hermann von Helmholtz
Both Helmholtz and Maxwell concentrated on selecting the most suitable diagram to explain the observed facts with regard to colour mixtures. Because the trichromatic theory was both available and accepted, their attention was turned towards the geometry of the triangle, without any consideration of the phenomenological aspects. However, after noticing that the spectral colours must have varying distances to white (which must, in turn, lie at the centre of the triangle),
Date: The colour diagram appeared in 1860 in the now famous Manual of Psychologocal Optics.
Country of origin: Germany
Basic colours: «Simple colours»: red, green and blue violet
Form: Modified triangle
Bibliography: H. von Helmholtz, «Manual of Physiological Optics», Volume II, Section 20 (1860); A. König and C. Dieterici, «Die Grundempfindungen in normalen und anomalen Farbsystemen», Zeitschrift für Psychologie 4, pp. 241-347 (1892); E. G. Boring, «Sensation and Perception in the History of Experimental Psychology», New York 1892.