Extra bands, usually pale pink or green in color, are often seen on the inside of the primary rainbow. They result from interference of light rays which emerge from water droplets in the same direction. While the primary rainbow colors result from a concentration of the different colored rays in the maximum deviation direction, there are many other paths for light through the droplets, so that at angles below the rainbow angle there could be rays of different wavelengths which emerge together. The number of visible supernumerary arcs depends upon the size of the raindrops.
Atmospheric optics concepts