The ice crystals forming this cloud gives an optical phenomenon which shows as a halo around the sun or moon. The cloud layer can be very thin and practically invisible for the eye. Its halo effect, however, clearly indicates its presence. The halo is normally white but can, as here, be very clear and display all the colours of the rainbow.

Since the light is very bright the sun is to be found behind the leaves and palm tree for photo technical reasons. The two photos are from the same occasion.

Same halo efffect but not as clear.

Since this cloud is formed at high altitudes, the halo effect can even be seen from a cockpit at 10000 metres.