Circumhorizontal arc?

An amazing sight today. Looking out my window at work, this colorful arc appeared I the sky. For about 5 - 10 minutes it continually changed shape and colors!
Purple, blue, green, yellow, orange, then turned red, and then turquoise!
It wasn't really a rainbow, but a prism of color in an arc. There was no rain, just a few clouds around it!
Awesome!