Fire rainbows are the rarest of all naturally occurring atmospheric phenomena. For a fire rainbow to occur, cirrus clouds must be feet in the air with the precise amount of ice crystals, and the sun must hit the clouds at 58 degrees. (a/k/a Sun Doggies)
This "fire rainbow," or iridescent cloud, was captured over South Florida. They are technically known as iridescent clouds, a relatively rare phenomenon caused by clouds of water droplets of nearly uniform size.