The 21-Feb-2016 BBC new article Singapore 'fire rainbow' cloud phenomenon lights up sky shows several photos of a rainbow-like iridescence in clouds on a sunny day in Singapore (about 1.3 degrees North latitude). Local time was about 17:10, 2 hours before sunset.
I've read about circumhorizontal arcs in this article, but the photos there (and other places) show a definite orientation - approximately parallel to the horizon with red on top (higher elevation angle).
However the photos from Singapore show tight circular patterns that resemble a color-coded contour map around a hill. So I think the explanation for these would not be identical to the explanation for a classic circumhorizontal arc or "Fire Rainbow".
below x2: Photo of the phenomenon seen in Singapore, from Singapore 'fire rainbow' cloud phenomenon lights up sky. Photo credit: Zhou Guang Ping.
below: example of a circumhorizontal arc from Fire Rainbows: A Rare Cloud Phenomenon.