Isaac Newton set out the colors of the rainbow we memorize today. However, he originally didn’t include orange or indigo. He only added them later because of his occult belief that there must be 7 separate colors, just like there are 7 notes in a musical scale and 7 days of the week.
Every rainbow is a circle, but from the ground, only its upper half can be seen. Pilots have noticed full-circle rainbows outside their plane windows, proving that if you get high enough, you can see a rainbow in its entirety.
To see a lunar rainbow or ‘Moonbow’, the moon must not only be full, it also has to be less than 42 degrees in the sky, within 2 to 3 hours before sunrise, and of course, there must be rain falling exactly opposite the moon at that precise moment.