What is colour?

Colour is more than just the property of objects and yet this is contrary to the way in which we use colour in everyday language. The association of colour with objects in our language, seen in statements such as ''this object is red", is misleading for it is undeniable that the colour that we perceive exists only in the brain.

It is commonly stated that colour vision is the result of the nature of the physical world, the physiological response of the eye (more strictly the retina) to light, and the neural processing of the retinal response by the brain. The identification of three separate processes in this way is probably artificial, and does little justice to the complex nature of colour perception, but the idea is useful and appealing since we shall see later that the number ``three" has an almost magical association with colour vision.

Source: http://www.colourware.co.uk/cpfaq.htm