There are many models used to measure and describe color. The RGB color model is based on the theory that all visible colors can be created using the primary additive colors red, green and blue. These colors are known as primary additives because when combined in equal amounts they produce white. When two or three of them are combined in different amounts, other colors are produced. For example, combining red and green in equal amounts creates yellow, green and blue creates cyan, and red and blue creates magenta.
As you change the amount of red, green and blue you are presented with new colors. Additionally, when one of these primary additive colors is not present you get black.
UNDERSTANDING COLOUR MODELS: