The defining qualities of a colour
Human colour vision is essentially 3-dimensional—you need three quantities or a solid 3-D model to describe the full range of colours that most people see. You can do this in many ways. There is the RGB system, the CIE system, the HLS system, the CMYK system… to name just a few of the sensible, coherent ways to describe a colour. Probably the easiest system to understand intuitively is the HLS system.
In the HLS system each colour is uniquely indentified by three characteristics—hue, luminance and saturation. These three characteristics can be visualised as the three dimensions of a colour sphere, which is best understood by first considering the colour wheel.
On a computer, it is convenient to describe colours using the additive primaries and to represent colour space as the RGB cube shown in the illustration on this page.