This strange cloud formations captured by eyewitnesses in Escazu Costa Rica, led many to believe that an unprecedented and possibly ominous phenomenon was happening right before their very eyes. But not to worry, these are pileus clouds, otherwise known as cap clouds, they form above towers of cumulus clouds giving an indication of the severe weather that is to come. The bright iridescent colors seen in pileus clouds are sunlight diffracted in water vapor. Iridescent colors are strongest when the diffracting droplets are small and similar in size.
This Strange Anomaly: Pileus Cloud Formation