Rainbow Clouds

We were returning to Blenheim after spending three days in Motueka. I had a number of images in mind that would be suitable for blipping. But as we neared Blenheim we noticed the lovely evening light on the Wither Hills. There were clouds hovering over the hills and as we were driving along we saw that these clouds were turning colours of the rainbow.
So we pulled over to the side of the road, grabbed our cameras and jumped out. It was too good an opportunity to miss. I have never seen this phenomenon before. I wonder if anyone has a term for this rainbow-like display in clouds…..