Colour Theory.

In the visual arts, colour theory is a body of practical guidance to colour mixing and the visual effects of a specific colour combination. There are also definitions (or categories) of colours based on the colour wheel: primary colour, secondary colour and tertiary colour. Although colour theory principles first appeared in the writings of Leone Battista Alberti (c.1435) and the notebooks of Leonardo da Vinci (c.1490), a tradition of "coloury theory" began in the 18th century, initially within a partisan controversy around Isaac Newton's theory of colour (Opticks, 1704) and the nature of so-called primary colours. From there it developed as an independent artistic tradition with only superficial reference to colourimetry and vision science.

http://en.wikipedia.org/wiki/Color_theory