Light from the sun or from any hot source is called white light. But, as Newton was the first to show, white light is really a mixture of light of all colours.
When a beam of light is made to pass through a glass prism, we see all the colours of the rainbow—red, orange, yellow, green, blue, and violet. Each shade blends gradually into the next without a break. This spread of colours is called a spectrum.
These colours are present in sunlight to begin with, but show up only after being spread out by refraction in the prism.
Each colour is refracted a slightly different amount, red least and violet most. This spreading is called dispersion. Without dispersion, the mixture gives the appearance of white to the eye.
A piece of red cloth, for example, absorbs almost all wavelength (the distance between two peaks) except a certain range of red ones. These are the only ones that are reflected to your eye, so you see the cloth as red.
So colour is a quality of light. It does not exist apart from light. All our colour sensations are caused by light rays entering our eyes.
All objects are seen by reflected light, and the colours that they show exist in the light and not in the object.
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