Lovely looking cactus!
Yeah, weather has been temperamental all over..sometimes plants just cope..agree with the comments above..leave it be. It should come back nicer eventually, as temps continue to warm up, then give it a drink, and should perk up once more. The graying thing is just the plant corking..showing its age..nothing to be worried about. It would be bad if the plant goes mushy..that will be a problem if it happens.