Their world is understood as an organic entity, with its colours arising from the continually observed struggle between the darkness of the night and the light of day. After sunset, this evening red becomes a purple violet, changing to a night sky which appears as dark blue. In between, green light can sometimes be seen. Plato observes that our eyes become filled with tears when we are too close to a fire. Tears, understood as the unity of water and fire, provide the eye's moisture, and eventually create mixtures which lead to the diversity of colours.
Objects thus acquire a radiance, and begin to glow.
If the tetrahedron is taken as a basis, three of these can be assembled, with their white tips interlocking around a central point to form a secondary triangular plane with a colour appointed to each of its corners. The white centre remains colourless and empty, attracting the tetrahedrons like a shadow, and allowing the colours to be mixed in the way familiar to us. Although he puts forward his construction as a rational theory of colour, Plato has not actually constructed a colour system, and the personal view presented here is only intended as an aid to understanding the colour mixtures he describes. Harmony has always been the object of our searching, and a corresponding number of colour theories have been passed down to us. A first colour system could be created by representing this system of harmony as a semi-circle which incorporates the traditional signs of the planets, and then adding the corresponding sequence of colours to this image.