White light can be produced by mixing different coloured lights together, the most common method is to use the primary colours red, green and blue (RGB). As this mechanism involves the blending and diffusion of different colours, this approach is little used for the production of white lighting due to the tendency of it to have a slight tint or hue. Nevertheless, this method is particularly interesting for effect applications because of the flexibility of mixing different colours.
In principle, most perceivable colours can be produced by mixing different amounts of three primary colours, and this makes it possible to produce precise dynamic colour control as well. Utilising the DMX control protocol, it is actually possible to achieve a colour palate of over 16 million shades!
How does this work? Well, on each colour scale it is possible to select 256 levels or shades of that colour. If you have three primary colours and each one can have 256 different shades, then by mixing them together you can mathematically generate 16.7 million different colours. 255 x 255 x 255 = 16,581,375.
RGB LED controllers work on a much simpler principal. They alter the power on each of the three channels (red, green and blue) to create a specific colour mix. To generate a purple colour, for example, the red and blue channels would be wound up, and the green channel turned off completely. Mixing blue and red light will give you the purple you are looking for. It is not as precise as DMX, but more than adequate for most residential and commercial applications where cost is a factor.