The History of Color Theory

In a darkened room in Woolsthorpe, Newton let a thin beam of sunlight fall on a glass prism and spread it across the wall. The decisive move was not the spreading — that had been seen before and dismissed as the glass 'staining' the light. It was the second prism. Newton isolated a single band of the fan, sent it through another prism, and found it refused to change. Red stayed red. The colors were not made by the glass; they were already in the light, and the prism only sorted them by how strongly each one bends.

That reframed white from a pure thing into a mixture, and it made color a measurable physical property: each hue has its own constant degree of refrangibility. Newton then did something stranger and more consequential for artists. He bent the linear spectrum into a ring, joining the violet end back to the red, and marked seven divisions on it — an analogy borrowed from the seven notes of the musical scale rather than anything the eye demands.

The circle let him predict mixtures geometrically: place weights at the hues being mixed, find the center of gravity, and the resulting point gives both the hue and how washed-out it is. It is the first color model in the modern sense — a space, with rules, that turns mixing into arithmetic.