Colour is simply light of different wavelengths.We are surrounded by electromagnetic waves of energy of which colour is a small part. All the electromagnetic rays are invisible to the human eye from the top of the spectrum - cosmic rays - to the bottom - radio waves - with the exception of the middle of the spectrum.

Visible light falls in the middle of the colour spectrum. In physics, the visible spectrum has three primary colours - Red, Green and Blue violet; chemically, colour is derived from pigments and compounds and the three primary colours here are Red, Yellow and Blue.

Any two of these will give a third colour - a secondary colour. The sensory aspect of colour is visual and deals with the physiology and psychology. So here we see the two above systems in the perception of sight and there are then two combinations of three primaries, i.e. Red, Yellow and Blue and Red, Blue and Green. All other colours are derived from these.

The pyramid diagram shows the seven rainbow colours in order of their frequency, i.e. violet is at the top of the pyramid since it has the shortest wavelength and the highest frequency and red at the base with the longest wavelength and lowest frequency. These colours can be seen by passing light through a prism.

The three 'higher' colours of - Violet, Indigo and Blue are called the cool colours/ electric colours and generally indicate calm/coolness. The three 'lower' colours of Yellow, Orange and Red are called the warm colours/magnetic colours and generally warming, activating. The colour Green is the balance between the cool and warm rays.