There are 3 primary colors: red, yellow, and blue.

Why are they called primary colors?
Because they are the colors from which all other colors are made.

Look for the primary colors in these paintings:

Fritz Glarner,          Relational Painting,          Tondo #40		Sol LeWitt, Four Geometric Figures in a Room
Elsworth Kelly,           Red, Green, Blue		George Sugarman, Yellow Top
Morris Louis, #28		Adolph Gottlieb, Trio