A rainbow is a meteorological phenomenon. It results in a spectrum of light appearing in the sky.

When a sunbeam is being refracted twice and reflected once by the droplet, a primary rainbow will form. It is also by dispersion of light.  It takes the form of a multi coloured circular arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun.

In a primary rainbow, the arc shows red on the outer part and violet on the inner side. 

Apart from primary rainbow, there is secondary rainbow also. If the beam is being refracted twice and reflected twice, a secondary rainbow will form.

As the secondary rainbow is formed by one more reflection than the primary rainbow, it is much fainter and rare to see. On the other hand, since the paths of sunbeams in a primary rainbow and a secondary rainbow are different, the colours of the secondary rainbow are arranged in just the reverse order of the primary one.