We are surrounded by electromagnetic waves of energy of which colour is a small part.
Visible light falls in the middle of the spectrum.
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.