The first parallel does not imply that the wavelength of a hue should correspond to the wavelength of a pitch. The physics of color is so far removed from the physics of sound that there is no physical basis for any such scheme. Pitch-to-hue correspondence schemes have been put forth by synaesthetic artists, as Scriabin was purported to be, but the synaesthetic response of a rare individual certainly cannot provide a solid a basis for an artistic medium. The same can be said of intuitive schemes created by mystics and various artists. The electronic 'color organs' popular in the '70's that activated colored lamps based on sound signals processed through notch filters did not contribute to the emergence of a kinetic color medium because the pitch-to-hue correspondences produced are the convenient output of the circuitry, and are not related to the process of seeing.

B)     For the second dimension, loudness, understood as the abundance of sound, is parallel to color intensity, understood as the abundance of light.

C)     The third parallel is the most difficult. The wave structure of sound produces harmonic interactions that are not present in visible light. What parallel visual dimension can fulfill the powerful role that harmonics play in sound? Such a dimension must be as deeply intrinsic to color as harmonic interactions are to musical sound. I have suggested that perceptual contrast phenomena, to a great extent, fulfill a parallel role to harmonics.

   Music, insofar as it entails melody and harmony, comes directly from the harmonic structure of sound. Most humans have an audible range greater than nine octaves, and each octave is filled with a multitude of possible harmonic interactions between the sound waves. When two or more pitches are played simultaneously, their sound waves interact according to the harmonic relationship between the frequencies, and the wave interactions produce characteristic sounds. In the case of sequential pitches, as in a melody, the harmonic relationship between each pair of sequential pitches determines the character of the tonal interval. The progression of music in time is molded by its development toward or away from simple harmonic ratios.

    Visible light waves comprise less than one octave, with wavelengths ranging from 400 nm to 700 nm, and no wave interference effects are observed when multiple frequencies overlay each other. These two facts require the abandonment of any plan for translating sound frequencies into colors.

    Color interactions, instead of occurring between the waves, are determined by perceptual contrast mechanisms. Visual perception of a color area produces a multi-layered perceptual inhibition response, which results in color distortions. These have been described by Goethe, Chevreul, and Albers. I appreciate Albers' writing and examples in Interaction of Color because it is addresses the need of artists to understand the behavior of color.

    When a color is exposed to an area of the retina, the color is perceived, and simultaneously a strong perceptual inhibition mechanism is initiated. Perceptual inhibition protects vision from excessive stimulus, but it also creates emphasis of any changes in the field of vision, a valuable survival mechanism. Inhibition of the stimulated receptors causes an imbalance in color perception that favors the color receptors that are not stimulated. When the stimulant is removed, the imbalance results in an illusory perception of the "anti-hue" of the stimulant, or the complementary color - the afterimage. The afterimage combines with any new color presented to that area of the retina, shifting the perception of the new color toward the compliment of the initial stimulant, causing the new color to appear to be more different from the original color than it actually is. This is sequential contrast.

    The inhibition of stimulated receptor cells in the retina spreads through lateral tendrils of the neurons. You may have noticed that afterimages are fuzzy. At the edge between two color areas this lateral spreading of the complementarity in the receptors combines with the adjacent color causing the edge to appear to have greater contrast. This is simultaneous contrast.