This is a rare natural phenomenon known as a rainbow cloud or fire cloud. I photographed it last July from Bukit Beruntung near Federal Route 1. It was my second time seeing and photographing this beautiful weather phenomenon. The first time was from the old Bentong road.
I discovered something new when I re-opened the image in the updated Photoshop software today. Rainbows and cloud rainbows benefit greatly from the new Dehaze filter in Photoshop CC 2015. The rainbows colours became more vivid and clearer when Dehaze was deployed under Camera Raw Filter.
With another image of a regular rainbow arc, I was able to bring out the so-called double arc or secondary rainbow that was otherwise invisible. There is payload though. It is at the cost of noise increasing in the blue spectrum, especially that of the sky.
Sony Alpha a7R, ISO 100, f11, 1/1000 sec.