The linked article below explains how this cloud colouring occurs.

I saw a cloud with rainbow colors. What causes it?

https://earthsky.org/earth/i-saw-a-cloud-with-rainbow-colors-what-causes-it?fbclid=IwAR0Pc0S1BwgTwTTUEe5Hvjr8T7BlHtTabYiSK6luuRkIJDwpzzHjP6WITo8

Thank you to Susan Woodhouse on Facebook group “Weather Obsessed” for providing the link