[Hippy Witchy Chicky]

According to this book: The Encyclopedia of Energy Healing by Andy Baggott

The mental body..
This body forms an outer layer around the astral body and is the same oval shape. It is colored blue, turning to purple as it rises up to the body. In spiritually evolved individuals, this body is colored white, silver, or gold above and around the head, depicted as a halo in medieval art.

Now, I don't agree with the books explanation of the astral and etheral bodies at all, however I thought it was interesting how the halo was explained. I do think there is something to that!!