Note on the diagram of the color wheel that each of the three colors cyan, magenta, and yellow are opposite one of the additive primary colors: red is opposite cyan, green is opposite magenta, and yellow is opposite blue. These pairs are called complementary colors.
For example, if you take white light and filter out red, the result is cyan; if you take white light and filter out blue, you get yellow.
You can use the CMY model, like the HSV and RGB models, to characterize any color by specifying the amount of cyan, magenta, and yellow. The three values of a color in the CMY system are the opposite of the values in the RGB system. If each value is expressed as a value between 0 and 1, the C value of a color is (1-R), and also M = (1-G) and Y = (1-B).
These colors are sometimes called the subtractive primary colors: if you start with white light, you can filter out various amounts of cyan, yellow, and magenta to produce any color.