Tertiary colors are intermediate colors that are made by mixing equal concentrations of a primary color with a secondary color adjacent to it on the color wheel.
There are three primary colors - red, yellow, and blue; three secondary colors (made from mixing two primaries together in equal concentrations) - green, orange, and purple; and six tertiary colors - red-orange, yellow-orange, red-purple, blue-purple, yellow-green, and blue-green. It is traditional to name a tertiary color starting with the primary color first and the secondary color next, separated by a hyphen.
Tertiary colors are the steps between the primary and secondary colors in a 12-part color wheel. A 12-part color wheel consists of the primary, the secondary, and the tertiary colors as in the image shown, with #1 representing the primary colors, #2 representing the secondary colors, and #3 representing the tertiary colors. A 6-part color wheel consists of the primary and secondary colors, and a 3-part color wheel consists of the primary colors.
“By adjusting the proportions of the primary and secondary colors, you can create a wide range of subtle colors. Further intermediate colors can be made by repeatedly mixing each neighboring pair until you have an almost continuous transition of color.” (1)
The first color wheel was created by Sir Isaac Newton in 1704 after he discovered the visible spectrum of white sunlight when it passed through a prism. Seeing the sequence of red, orange, yellow, green, blue, indigo, and violet (known as the acronym ROY-G-BIV), Newton determined that red, yellow, and blue were the colors from which all the other colors were derived and created the color wheel on that premise, turning the sequence of colors back on itself to create the circle and show the natural progression of colors.
In 1876 Louis Prang advanced color wheel theory, creating the color wheel that we're most familiar with today, a simplified version of the pure hues of the spectrum (no tints, tones or shades), to explain color theory and to serve as a tool for artists to understand how to better mix colors and create the colors they want.
It was understood that colors relate to each other in two different ways: they either contrast or harmonize. The color wheel helps us visualize how colors relate to each other by their positions on the color wheel relative to each other. Those colors that are closer together are more compatible and harmonize better, producing more intense colors when mixed together, while those that are further apart are more contrasting, producing more neutral or desaturated colors when mixed together.
Colors that are adjacent to one another are called analogous colors and harmonize with one another. Those that are opposite one another are called complementary colors. These colors when mixed together result in a brownish hue, and one complement can be used to help neutralize or desaturate another.
For example, to create a tertiary color with yellow you can combine it with the secondary color between yellow and red, which is orange, to get yellow-orange or with the secondary color between yellow and blue, which is green, to get yellow-green.
To desaturate the yellow-orange you would mix it with its opposite, blue-purple. To desaturate yellow-green you would mix it with its opposite, red-purple.
If you were trying to mix an intense green you would use a cool yellow, like a yellow light hansa and a warm blue such as cerulean blue because they are closer together on the color wheel. You would not want to use a yellow-orange color, such as yellow-orange azo and an ultramarine blue because they are further apart on the color wheel. These colors have a bit of red mixed in with them, thereby combining all three primary colors in one mixture, making the final color a somewhat brown- or neutral-green.
Read Color Wheel and Color Mixing to find out how to paint your own color wheel using the cool and warm hues of each primary color to create a wide array of secondary colors.
Remember that the closer that different colors are on the color wheel, the more compatible they are, and the more intense the resulting color will be when the colors are mixed.
In 1810, Johan Wolfgang Goethe challenged Newton's assumptions about color and color relationships and published his own Theories on Color based on perceived psychological effects of color. In Goethe's Triangle the three primaries - red, yellow, and blue - are at the vertices of the triangle and the secondary colors are midway along the edges of the triangle. What is different is that the tertiaries are the neutral colored triangles created by combining a primary color with the secondary color opposite it rather than adjacent to it. Because this combines all the primary colors, the result is a variation of brown, and quite different than the commonly used definition of a tertiary color, which is more useful to painters. Rather, Goethe's tertiaries are what painters more commonly know as neutral colors.
1. Jennings, Simon, The Complete Artist's Manual, The Definitive Guide to Drawing and Painting, p. 214, Chronicle Books, San Francisco, 2014.