Cloud Iridescence is a diffraction phenomenon caused by small water droplets or small ice crystals individually scattering light. The colors are usually pastel pinks, greens, and blues arranged in smudges or orderly bands. The colors can sometimes be very vivid as they were here above Civetta in the Dolomites of northeastern Italy.
You can learn more about optical phenomena in the sky by clicking Celestial Lights to the right.
You can get to a page that will have links to 5 days of trekking in the Dolomites by clicking HERE. They are amazing mountains, very beautiful with dramatic shapes.