The colour is iridescence due to diffraction of sunlight. The sun is on or close to the horizon some ten-fifteen degrees below and behind the cap cloud.
Late sunset image. Pastel shades of iridescence 20 degrees from the setting sun in a layered pileus cloud (lenticular stack).
A rising cumulus encounters moisture laden wind layers just on sunset. The resulting Pileus clouds are back lit by the setting sun.
Tags: Pileus cloud cap cloud stack
Tags: pileus cap cloud
Multiple layers of slow moving moist air are lifted over the top of rising cumulus cloud. Adiabatic cooling forms a stack of thin lenticular clouds that persist for less than two minutes. The illumination is due to the diffraction of sunlight by relatively uniform small droplets.