It was a lunar halo, and is caused by the refraction, reflection, and dispersion of light through ice particles suspended within thin, wispy, high altitude cirrus or cirrostratus clouds. As light passes through these hexagon-shaped ice crystals, it is bent at a 22 degree angle, creating a halo 22 degrees in radius.
The prism effect of light passing through these six-sided ice crystals separates the light into its various colors, resulting in a halo tinged with very pale rainbow colors with red on the inside and blue on the outside. The phenomenon of a lunar halo is similar to a rainbow produced by sunlight and rain falling between your eye and the sun.
Here are a few pictures I took from my SLR camera ...
