Traditionally, the complementary color of yellow is purple; the two colors are opposite each other on the color wheel long used by painters.[13] Vincent van Gogh, an avid student of color theory, used combinations of yellow and purple in several of his paintings for the maximum contrast and harmony.[14]

Hunt defines that "two colors are complementary when it is possible to reproduce the tristimulus values of a specified achromatic stimulus by an additive mixture of these two stimuli."[15] That is, when two colored lights can be mixed to match a specified white (achromatic, non-colored) light, the colors of those two lights are complementary. This definition, however, does not constrain what version of white will be specified. In the nineteenth century, the scientists Grassmann and Helmholtz did experiments in which they concluded that finding a good complement for spectral yellow was difficult, but that the result was indigo, that is, a wavelength that today's color scientists would call violet or purple. Helmholtz says "Yellow and indigo blue" are complements.[16] Grassmann reconstructs Newton's category boundaries in terms of wavelengths and says "This indigo therefore falls within the limits of color between which, according to Helmholtz, the complementary colors of yellow lie."[17]

Newton's own color circle has yellow directly opposite the boundary between indigo and violet. These results, that the complement of yellow is a wavelength shorter than 450 nm, are derivable from the modern CIE 1931 system of colorimetry if it is assumed that the yellow is about 580 nm or shorter wavelength, and the specified white is the color of a blackbody radiator of temperature 2800 K or lower (that is, the white of an ordinary incandescent light bulb). More typically, with a daylight-colored or around 5000 to 6000 K white, the complement of yellow will be in the blue wavelength range, which is the standard modern answer for the complement of yellow.

Because of the characteristics of paint pigments and use of different color wheels, painters traditionally regard the complement of yellow as the color indigo or blue-violet.