Wiki says the colours aren't usually visible so this one was rare indeed.
A moonbow (also known as a lunar rainbow or white rainbow), is a rainbow produced by moonlight rather than sunlight. Other than the difference in the light source, its formation is the same as for a solar rainbow: It is caused by the refraction of light in many water droplets, such as a rain shower or a waterfall, and is always positioned in the opposite part of the sky from the moon relative to the observer.
Moonbows are much fainter than solar rainbows, due to the smaller amount of light reflected from the surface of the moon. Because the light is usually too faint to excite the cone colour receptors in human eyes, it is difficult for the human eye to discern colours in a moonbow. As a result, a moonbow often appears to be white.[1] However, the colours in a moonbow do appear in long exposure photographs.
