Although I consider contrast to be a more useful guide to the student-artist, the artist, and the designer, harmony and contrast in color are not mutually exclusive. Every outstanding artist and color theorist involved in the color revolution of the nineteenth century--Delacroix, Chevreul, Charles Blanc, Charles Henry, Hermann von Helmholtz, David Sutter, Rood, Seurat, and others--placed special emphasis on the harmony of complementaries. Blanc, in his article on Delacroix, states that "New contrasts could be born of the juxtaposition of two complementaries, of which one is pure and the other modified. The struggle being unequal, one of the two colors triumphs, and the intensity of the dominant one does not hinder the harmony of the pair." Delacroix, according to Blanc, was one of those artists who combined great sensitivity of artistic vision and theory; that, perhaps, is the reason he remained the unique hero of colorists who came after him: Seurat, Signac, van Gogh, Pissarro, and Matisse in particular. Blanc says that Delacroix "pursued unity in the interpenetration of opposites. Bringing together all the facets of green, all the variants of red, he modified them, mixed them together, provided them with weakened echoes or redoublings of force, and composed of them a harmony mordant for the mind, caressing for the eyes." [33] Delacroix, like Turner, was a kind of impressionist, in that he understood color as energy and therefore the relationship of luminosity [the role of a certain amount of optical blending] to radiance [vibrant colors, whether employed in large or small amounts]. [Monet once said: "All the great painters were more or less impressionists."]
If indeed it is true that contrast provides us a better guide through the intricacies of color, it is probably due to the fact that there are more kinds of contrast about which we can be reasonably certain. [p. 110]
[Harlan, Calvin Vision & Invention, An Introduction to Art Fundamentals. Englewood Cliffs, NJ 07632: Prentice-Hall, Inc., 1986.]