As the cumulonimbus cloud at bottom began to rapidly grow a golden pileus cloud took shape — at left. The beautiful iridescent colors were clearly visible for about 10 minutes. In order for iridescence to occur cloud droplets in the vicinity of the Sun must, in general, have similar sizes and be randomly spaced. If the droplets are nearly identical in size the resulting colors may be particularly pure.
Image © Raqqasah Shruti Chakravarti