Color wheel
[5] The original color circle of Isaac Newton showed only the spectral hues and was provided to illustrate a rule for the color of mixtures of lights, that these could be approximately predicted from the center of gravity of the numbers of "rays" of each spectral color present (represented in his diagram by small circles).
[6] The divisions of Newton's circle are of unequal size, being based on the intervals of a Dorian musical scale.
[7] Most later color circles include the purples, however, between red and violet, and have equal-sized hue divisions.
[9] Thomas Young postulated that the eye contains receptors that respond to three different primary sensations, or spectra of light.
Goethe's Theory of Colours provided the first systematic study of the physiological effects of color (1810).
Non-digital visual artists typically use red, yellow, and blue primaries (RYB color model) arranged at three equally spaced points around their color wheel.
A color wheel based on RGB (red, green, blue) additive primaries has cyan, magenta, and yellow secondaries.
Alternatively, the same arrangement of colors around a circle can be described as based on cyan, magenta, and yellow subtractive primaries, with red, green, and blue being secondaries.
The HSL and HSV color spaces are simple geometric transformations of the RGB cube into cylindrical form.
A color circle based on spectral wavelengths appears with red at one end of the spectrum and is 100% mixable violet at the other.
A wedge-shaped gap represents colors that have no unique spectral frequency.
Combining two colored lights from different parts of the spectrum will produce a third color that appears like a light from another part of the spectrum, even though dissimilar wavelengths are involved.
[14] Thus, a combination of green and red light will produce the color yellow in apparent hue.
Arranging spectral colors in a circle to predict admixture of light stems from work by Sir Isaac Newton.
The psychophysical theory behind the color circle dates to the early color triangle of Thomas Young, whose work was later extended by James Clerk Maxwell and Hermann von Helmholtz.
For example, the use of a white background with black text is an example of a common default color scheme in web design.
