This is an image captured by August Allen in Boulder, Colorado.

It wasn’t until I saw this picture that I realized clouds could be as colorful as rainbows. Cloud iridescence is a fairly rare natural phenomenon in which clouds near the sun show a spectrum of colors simultaneously.

It is actually a diffraction phenomenon caused by small droplets and ice crystals respectively scattering lights. That explains why observers are able to see different colors from different directions.

Cloud iridescence is most likely to be observed when the sun is hidden by thick clouds but it quickly becomes invisible when clouds turn too thick or drift too far away from the sun.

Aesthetically, the image is also valuable. When such an uncommon scene is captured, people know more about the world we are living in. And the beauty of nature also encourages people to engage themselves in oberserving the myths of our environment.

http://apod.nasa.gov/apod/ap071125.html