Rudolph the Red Nosed Dime

I have a 2000 S silver Proof Roosevelt dime that the face has turned a rich rust RED color and Roosevelt's nose is really red.

It is still in the original Mint proof case and came with a silver proof set. The raised areas (primarily the head) including the lettering has turned this Deep color while the cameo portion is 100% like normal. This seems strange to me.

The picture is a scan and has some trash on the scanner and on the plastic case that the coin is in. Does anyone have any suggestions.

Thanks, Lamar