Iridescent Clouds over Mérida, Spain
Image by Rothkko
Cloud iridescence is the occurrence of colors in a cloud similar to those seen in oil films on puddles, and is similar to irisation.
It is a fairly uncommon phenomenon, most often observed in altocumulus, cirrocumulus and lenticular clouds, and very rarely in cirrus clouds. The colors are usually pastel, but can be very vivid. Iridescence is generally produced near the sun, with the sun’s glare masking it, so it is more easily seen by hiding the sun behind a tree or building.
Other aids are dark glasses, or observing the sky reflected in a convex mirror or in a pool of water. [**]