Color is an effect caused by the reflection of certain rays of light. In order to understand this statement, it is necessary that we know what light is. Science teaches us that light is a form of intense vibration which reaches the earth direct from the sun. These vibrations affect certain nerves of the retina of the eye, causing the sensation known as color.

In the study of color, or in practice, it is necessary that we have a standard. The standard colors are those seen in the spectrum or in the rainbow. These colors are selected as standard colors because they are the true colors as reflected by pure light and they never change.

In dealing with pigments the primary colors are yellow, red and blue. They are called primary colors because all other colors are produced from them, and because they can not be produced by mixing other colors. In other words, they are the original colors from which all other colors are produced.