White light is made of an infinite number of different colours, from violet at one end through to red at the other. This band of visible colours is known as the spectrum. Light at the blue end has a shorter wavelength and higher frequency than light at the red end. Most people can see only seven distinct colours in the spectrum: red, orange, yellow, green, blue, indigo, and violet.
Just as a prism can split white light into different colours, so lights of different colour can be added together to make white light. If three torches shine red, blue, and green light together, the colours combine to make white light. Yellow light appears where the red and green lights overlap. Magenta occurs where the red and blue lights meet. Cyan appears where the blue light meets the green.
The colours of a rainbow are made when sunlight shines through raindrops. When a ray of sunlight enters a raindrop, the tiny drop of water splits up the white light into different colours. Although a rainbow usually looks semicircular from the ground, it appears as a complete circle if you look at it from an aeroplane.
Objects look coloured because they reflect or absorb the different colours in white light. A golf ball looks white because it reflects all the wavelengths of light that fall on it. A lemon absorbs all wavelengths of light except yellow, which it reflects into our eyes. A black helmet absorbs all wavelengths of light and reflects none, and so it looks dark to us.
Coloured inks and paints (sometimes called pigments) mix in a completely different way to coloured lights. Each pigment reflects light of a different colour. When two coloured pigments are mixed together, the number of colours they can reflect is reduced. When three pigments are mixed, the mixture does not reflect any colours and appears a brownish black.
Picture Credit : Google
