In color theory for artists, the secondary colors—green, orange, and purple—are created by mixing two primary colors. The ratio of primary colors you use when you mix will determine the final hue of the secondary colors.
Mixing Secondary Colors
At its most basic, color theory tells us that if we mix equal parts of two primary colors—blue, red, and yellow—we will create either green, orange, or purple. This is the foundation for the color wheel and a lesson that is often taught in elementary art classes.
Blue and yellow make green.
Yellow and red make orange.
Red and blue make purple.
The secondary color you actually get will depend on the proportion in which you mix the two primaries. For example, if you add more red than yellow to a red-yellow mix, you get a reddish orange, and if you add more yellow than red, you get a yellowish orange.
When we take this a step further and mix a primary color with a secondary color, we get a tertiary color. There are six of these shades and they're the compound colors known as red-orange, blue-green, etc.
Primary Hue Matters
Artists know that there is more than one option when it comes to primary color paint choices. This will affect the hue of your secondary color. For instance, a purple made of cerulean blue and a medium cadmium red will be different than the purple you get from mixing cobalt blue and that same cadmium red.
These differences may be subtle, but it is important to be aware of them. One thing that many artists find helpful is to make a paint sample in a notebook with the colors mixed and the ratios they've used to obtain that color. It takes a lot of the guesswork out of trying to reproduce a particular hue the next time you want to paint with it.
Colors That Complement Secondary Colors
Diving a little deeper into color theory, we also learn that every color on the color wheel has a complementary color. For each of our three secondary colors, the complementary color is the one primary color that was not used to create it. Knowing this can help you in choosing a good paint to make your secondary colors appear brighter and in choosing shadow colors for objects.
The complementary color of green is red.
The complementary color of orange is blue.
The complementary color of purple is yellow.
Additive vs. Subtractive Secondary Colors
Did you know that this is not the only color system in use? When mixing paint, we are actually using subtractive colors. This means that we are subtracting one of the primary colors out of the equation that would create black. It is the traditional way of thinking about mixing colors.
Thanks to technology, some artists also have to deal with additive colors. This is true if you create artwork on the computer or work in graphic design. Additive colors are based on light instead of pigments, so mixing begins with black and builds up color until the color gets to white. In this system, red, green, and blue are the primaries, and the secondary colors are cyan, magenta, and yellow.
This can be a little confusing, especially when generically trying to define "secondary colors." However, as long as you understand the medium being used—paint versus light—it's relatively easy to remember.