RYB colour model
RYB (an abbreviation of red–yellow–blue) is a historical set of colors used in subtractive color mixing and is one commonly used set of primary colors. It is primarily used in art and design education, particularly painting.
Mixture of RYB primary colors
RYB predates modern scientific color theory, which has determined that cyan, magenta, and yellow are the best set of three colorants to combine, for the widest range of high-chroma colors.
A color wheel or colour circle is an abstract illustrative organization of color hues around a circle, which shows the relationships between primary colors, secondary colors, tertiary colors etc.
As an illustrative model, artists typically use red, yellow, and blue primaries (RYB color model) arranged at three equally spaced points around their color wheel. Printers and others who use modern subtractive color methods and terminology use magenta, yellow, and cyan as subtractive primaries. Intermediate and interior points of color wheels and circles represent color mixtures. In a paint or subtractive color wheel, the “center of gravity” is usually (but not always) black, representing all colors of light being absorbed; in a color circle, on the other hand, the center is white or gray, indicating a mixture of different wavelengths of light (all wavelengths, or two complementary colors, for example).
Boutet’s 7-color and 12-color color circles from 1708
Claude Boutet’s 1708 color circle uses the same arrangement of primary and secondary color names as modern RYB color circles.
Source: Traité de la peinture en mignature (The Hague, 1708), reproduced in The Creation of Color in Eighteenth-Century Europe.