Color is all around us. Theorists like Birren believed that color's influence extended beyond simply being a source of mere pleasing perception to having a fundamental influence on artwork, human psychology and the workplace experience. He believed that color was a primary tool of expression, communication and self-identification. In his introduction to "The Elements of Color," Birren wrote that "Expression should come from within," albeit from a conscious, informed perspective.
Birren links the human perception of color to the emotional response it evokes in the viewer. He explains, in his 1961 publication, "Creative Color: An Approach for Artists and Designers," that people associate color with other senses. He writes, "Good smelling colors are pink, lilac, orchid, cool green, aqua blue," and goes on to describe the associations of other colors with corresponding senses. The association of one sense with another is known as synaesthesia. In "Color Psychology and Color Therapy," Birren observes that introverts tend to be unresponsive to color, and that emotionally responsive people react more readily to color.
Birren did not agree with the ideas of Fauvists, whose replacement of sensitive, accurate colors with raw, undiluted color sometimes rendered their paintings garish and bold. Birren's system of color harmony employed tints, tones and shades, which are all dilutions of colors. A tint is made up of a pure color combined with white; a tone is made up of a pure color in combination with gray; and a shade is formed from mixing black with a pure color. Birren posited that harmony could be constituted by any qualities in the diagram (see above) that were connected by an approximately straight line.
In his book, "Creative Color," Birren wrote that "Almost any orderly sequence of color will appear pleasing to the human eye." Birren believed that warm colors are preferred over cool colors by many artists, and in his diagrams of color harmonies, he afforded more weight to warm tones. One artist that, according to Birren's idea of harmony, made use of his system was Leonardo, whose chiaroscuro comprised a tint-tone-shade combination that rendered it harmonious.
Birren's most prominent color theory contribution is known as perceptionism. In perceptionism, an attempt to produce color results that are life-like will be the most successful with palette that is restricted according to the "field size." According to Anthony Holdsworth, "The largest areas of a canvas must establish a field that
keys the smaller elements. Generally speaking, this field is of lower saturation than the smaller, active areas." Notably, perceptionism's effects are judged independently of realism.