Turner created only two diagrams dealing with colour theory. He used them in a lecture on atmospheric perspective: the use of colour, light and shade to lend a picture a sense of depth.

This diagram illustrates the behaviour of colour in light. Turner used it to address colour symbolism of the times of day, explaining that the upper and lower portions of the diagram represent the light and dark of day and night. He told his students ‘suppose the yellow triangle light, red and blue shade; and hence we have grey morning, the yellow midday and crimson evening’.