If the polyps are open and it looks full I wouldn't worry too much,it's probably just getting use to the tank,water parameters. Might have been different from where you got it from.Colt's are very hardy as most soft corals are
Put the whole bag in the water with lights off for 30 min, then put a little water in the bag let sit for another 15 min. Stuck his base in a rock on the sand bed and started turning lights on slowly actinics first then hour later 10,000ks. I've even moving him closer to the top since I got him, now he is at the top of the tank.