Dispersion
The index of refraction of a medium depends in a slightly manner on the frequency of the light-beam
Different color rays deflect in different manner during refraction: violet light is deflected more than red…..
By refraction we can decompose the white color in its constituents--> A prism separates white light into the colors of the rainbow: ROY G. BIV
We can do the opposite effect too…..recombining the rainbow colors in white light
Atmospheric dispersion of light: rainbow (dispersion on tinny water drops) or halos (dispersion on tiny ice crystals)