The tri-stimuli model of colour perception is generally accepted. It states that there are three degrees of freedom in the description of a colour. Various three-dimensional spaces are used to describe and define colours. For our purposes, the following three are sufficient:
Red-Green-Blue (RGB) space, which is based on the additive mixing principle of colour;
Intensity-Hue-Saturation (IHS) space, which most closely resembles our intuitive perception of colour;
Yellow-Magenta-Cyan (YMC) space, which is based on the subtractive principle of colour.