The three primary colors are red, green and blue. When red light, green light and blue light are mixed together in equal proportions, they combine to form white light.
In traditional color theory, red, yellow and blue are considered to be the three primary colors. However, these colors cannot be mixed together to create as many different colors as red, green and blue, due to the way in which human vision works.
The printing industry uses a subtractive model of color in which cyan, magenta and yellow are the three primary colors. When these three colors are mixed together, the result is black.