Psychologically Pure Colors

Psychologically pure colors are colors that exhibit a homogeneous appearance on some dimension of perceived color. Purity of appearance is closely tied up with theoretical understandings of the three canonical color attributes of hue, saturation, and lightness. According to the dominant Hering opponent color framework, the hues red, green, blue, and yellow are distinctive and fundamental to all hue perception, in part due to the fact that they admit of pure or unique variants and all other hues (such as orange) appear as mixtures of them. Saturation and related notions are characterized essentially in terms of purity, involving judgments regarding differences in the appearance of chromatic stimuli and achromatic stimuli. Highly saturated colors appear to have low achromatic content or to be more intensely chromatic. In the achromatic domain, the lightness dimension runs from light to dark. The corresponding extreme ends of that dimension, white and black, have an appearance that wholly excludes the other, while intermediate steps between them are grays that appear to be mixtures of black and white. The concept of purity plausibly could also be usefully applied in connection with other ways of categorizing perceived color, e.g., warm versus cool and positive feeling versus negative feeling.