If two of the primary colors are mixed together, a secondary colour is created. As more colors are mixed, the selection of colors grows.

Usually Secondary colours are additive colours which can be produced by mixing two primary colours in different proportions. The additive primary colours are Red, Green and Blue. When these additive colours are mixed, they produce three other secondary colours. These are: (1) Cyan; (2) Magenta; (3) Yellow.

We use subtractive primary colours when we are mixing paints or inks. In the case of inks and printing, the colours used are Cyan, Magenta, Yellow and black. (CMYK for short). When we mix all the secondary colours we get black colour.

Complementary Colors of Light Any two colors of light that when mixed together in equal intensities produce white are said to be complementary colors of each other. The complementary color of red light is cyan light. This is reasonable since cyan light is the combination of blue and green light; and blue and green light when added to red light will produce white light. Thus, red light and cyan light (blue + green) represent a pair of complementary colors; they add together to produce white light.
Complementary Colors of Light are (1) Red and Cyan; (2) Green and Magenta; (3) Blue and Yellow
The production of various colors of light by the mixing of any two primary colors of light is known as color addition.