Iridescent clouds are clouds colored in the colors of spectra in the vicinity of a light source. The phenomenon is very common.
Like a corona, a clouds of color are formed when light is scattered in small water droplets. Fineest colors are seen in cirrocumulus and altocumulus lenticularis-type clouds. The more mundane-looking color clouds, on the other hand, are lower clouds.
Like coronae, color clouds usually occur only very close to the Sun. Their colors are more clearly visible through sunglasses.
The word "iridescent clouds", clouds with colors, may sound the same as any colored cloud that exists. However clouds colored reddish by morning or evening dusk are not the same thing. The ridescent clouds specifically show the full color of spectrum. The iridescent clouds are not a synonym for the also colorful mother-of-pearl -clouds. These polar stratospheric clouds are a different phenomenon that occurs and very low winter temperatures hight in the atmosphere.
Cloud iridescence on altocumulus lentocularis. Photo by Panu Lahtinen.
Colors of spectrum on an altocumulus cloud. Image by Matti Helin.
Iridescent Stratocumulus cloud. Photo by Panu Lahtinen.
Sometimes it may be difficult to determine, if the colors on the cloud belong to a corona or cloud irridescence. This one could be marked with either one or both of the phenomena identifications. Image by Marko Myllyniemi.