A rainbow is formed when light is the Moon, not the Sun. Despite the fact that the optics of both is the same, the brightness of a lunar Rainbow is much lower. As a result of reduced sensitivity to eye color in low light bow can be a little color. There are several reasons why the Lunar Rainbow is observed much less frequently than the solar bow. Although the Moon and the Sun to spend equal time on the horizon when they both present, you can see only the solar bow. This, in itself, means that Lunar rainbows can be only half as often. The Moon goes through phases and so even at night can lead to enough light to get a good bow. Finally convective showers, which is often much less Rainbow seen at night.