These have been identified on iNaturalist as a species of Cycloseris but I think that needs verification. Like a few other species, some polyps glow with orange deeper than orange light from the sun penetrates. Most of our specimens were photographed on the seaward reef, although we have seen them in the lagoon as well. Those figured are all small, no more than about 40mm diameter.
Some of these orange and bright green colors fluoresce underwater and are seen at depths greater than those colors penetrate from sunlight. It has been discovered that proteins in the coral tissue absorb light at the longer, bluish wavelengths and re-emit it at shorter, orange or bright green wavelengths. The orange or green glow is very distinct at depth, but gets completely washed out if you try to take a flash photograph of it. The next two shots show the same coral, the first taken with underwater flash shows the coral to be yellow, but the second, taken without flash and the way a diver sees it with available light, shows the bright orange glow.
Below is another pair of photos of the same coral, the first with a flash and the second with available light.
Created 10 April 2020
Updated 8 June 2023