A tertiary color is a color made by mixing either one primary color with one secondary color, or two secondary colors, in a given color space such as RGB (more modern) or RYB (traditional).

Tertiary colors have specific names, one set of names for the RGB color wheel and a different set of names and colors for the RYB color wheel. These names are shown below.

Brown and grey colors can be made by mixing complementary colors.

The primary colors in an RGB color wheel are red, green, and blue, because these are the three additive colors—the primary colors of light. The secondary colors in an RGB color wheel are cyan, magenta, and yellow because these are the three subtractive colors—the primary colors of pigment.

The tertiary color names used in the descriptions of RGB (or equivalently CMYK) systems are shown below.

The primary colors in an RYB color wheel are red, yellow, and blue. The secondary colors in an RYB color wheel are made by combining the primary colors--orange, green, and violet.

In the red–yellow–blue system as used in traditional painting, and interior design, tertiary colors are typically named by combining the names of the adjacent primary and secondary.

In the visual arts, color theory is a body of practical guidance to color mixing and the visual impacts of specific color combination. There are also definitions (or categories) of colors based on the color wheel: primary color, secondary color and tertiary color. Although color theory principles first appeared in the writings of Leone Battista Alberti (c.1435) and the notebooks of Leonardo da Vinci (c.1490), a tradition of "colory theory" began in the 18th century, initially within a partisan controversy around Isaac Newton's theory of color (Opticks, 1704) and the nature of so-called primary colors. From there it developed as an independent artistic tradition with only superficial reference to colorimetry and vision science.

The foundations of pre-20th-century color theory were built around "pure" or ideal colors, characterized by sensory experiences rather than attributes of the physical world. This has led to a number of inaccuracies in traditional color theory principles that are not always remedied in modern formulations.^{[citation needed]}