This is a starfish that eats the reef and kills it. So it is destructive and should be killed on sight. You can’t cut it up. Each piece will generate a new starfish. It is colorful because strobe lighting will make it so.
Otherwise it is drab gray underwater. I dragged this guy out from under the coral and laid it over an outcropping. It then lazily unfolded and moved away. This is only the second time I have seen one in this area of the reef. So I guess most of the coral is still safe.