Chingis A. Izmailov (variant: Chingiz A. Izmailov; in Russian: Чингиз Абильфазович Измайлов) (March 26, 1944 – September 28, 2011) was a Russian psychophysiologist and psychophysicist, the principal author of the spherical model of color space. Biography Chingis Izmailov was born in Derbent, USSR, in 1944. He first studied art and architecture in Moscow, then, in 1971, joined the department of Psychology of the Lomonosov Moscow State University, and in 1976 the same department's graduate school. In 1979 Chingis Izmailov got his PhD in psychology for his development of the spherical model of color space (with E. N. Sokolov as his scientific adviser), in 1985 was awarded his “big doctorate” (доктор наук, a Russian equivalent of the German Habilitation) for his work on color vision mechanisms and models. Chingis Izmailov was a professor at the Lomonosov Moscow State University since 1987, Distinguished Professor since 2005. He was a member of the central council of the International Brain Research Organization at UNESCO, participated in many professional societies, developed and taught many courses in color science, psychophysiology, psychophysics, and quantitative methodology. Chingis Izmailov died in 2011 after prolonged illness. Work Chingis Izmailov's main achievements are in the field of color science, but he also contributed to other areas of psychophysiology and psychophysics, such as multidimensional scaling of geometric shapes and emotions in facial expressions. His experimental work and mathematical models were primarily based on various forms of multidimensional scaling, and on amplitudes of evoked potentials in humans and electroretinogram in frogs in response to an abrupt change of one stimulus to another. Izmailov's model of color space represents both aperture and pigment colors as points on a four-dimensional sphere, such that the Euclidean distance (chord length rather than arc length) between two colors is nearly proportional to the estimates of their dissimilarity. Two axes of the sphere correspond to the color-opponent channels (red-green, blue-yellow), the other two axes represent the achromatic “whiteness” and “darkness” channels which Chingis Izmailov distinguished from brightness. The model allows one to quantitatively describe contrast and adaptation phenomena, as well as individual differences and color anomalies. In particular, the model provides a way of quantifying a spectrum of color abnormalities from the very mild anomalous variations to severe deficiencies, like protanopia and deuteranopia. Chingis Izmailov also studied the phylogenetic development of color vision, the emergence of saturation as a “composite” property from more basic circular color spaces, and the