The rule of refraction is, the shorter the wavelength, the greater refraction and the longer the wavelength the smaller the refraction. The seven colours of the rainbow are ordered from the greatest to the smallest refraction; violet, indigo, blue, green, yellow, orange, and red.
‘Newton gave the name “spectrum” or “iris” to the progression of colors, and “dispersion” to the separation or decomposition of the individual color of white light.’
The colours of the spectrum are monochromatic and are able to be broken down as there is only one wavelength. The rays of the spectrum stay the same when isolated.
‘Newton’s color circle. The size of each sector corresponds to the extension of the respective color over the spectrum, their number to the number of colors that the eye manages to see.’
‘Newton, who includes indigo as “fundamental” because it appears among the clearest colors of the spectrum, subdivides the circle into seven parts, possibly because of its analogy with musical notes.’