Sandra Kerrest (Member 61,692) spotted what looked like an oil slick in the sky beyond the dark mounds of Cumulonimbus calvus storm clouds that towered over Stuart, Florida, US. The scene appeared to Sandra ‘as though there were a hole in the sky, on the right of the rose-colored part of the cloud…where the bright blue shone through’. The soft hues are known as cloud iridescence. They are appearing here in a delicate cap of cloud, known as a pileus, that can appear over the top of building storms. The sunlight is diffracted by extremely small supercooled water droplets in the cloud. Since these are short-lived, they’re all similarly sized, and this means their effects on the light all add up to form a shimmering slick of pastel hues that is spread across the sky.