Is the bluish haze on the bust of some Kennedys the result of doctoring?

mdwoods

I have seen several slabbed Kennedy half dollars with a bluish-gray haze on the bust of Kennedy. Usually it is visible only at a certain angle. Is this a natural toning, or is it a sign of tampering? Thanks, mdwoods

CarlWohlforth

I think that is natural. I have seen that on lots of proof Eisenhower dollars too, some still in proof sets.