Colts, kenyas, and other
soft corals in this family are know to get ticked off, deflate, and cease to expand for a few days. This is normal. It is also quite common for any coral's color to fade when the lights go off or change. My red mushrooms turn green when the lights go off and my colt fades to a greyish pale color.
Watch it closely. If it was dead, it would smell horrible. I would watch it over for a few more days and consult us here if its condition does not improve.
Have you changed you lighting , flow around the coral or generally in the tank, or filtration methods by any chance? Have you added any new critters or corals to the tank recently?
HTH