|Iridescent Fractus ~ Images by Sam Reynolds taken at the East End of Grand Cayman Island. ęSam Reynolds, shown with permission.
Optical effects can be very transient. Here a gap in the towering cumulus gives a ray of sunlight. It happens to shine on a lower level cloud fragment. The fragment was likely recently formed because it just happens to have small water droplets all of roughly similar size. They diffract sunlight towards the camera to give the iridescent colours.