That's not an error. That is a damaged coin. 1976 cents are a copper-zinc alloy. They are not plated. In order for a coin to have 2 distinct colors such as yours, something had to happen to it after it left the mint. It could be paint. Try soaking it in pure acetone. It might come off .
(1) Not the slightest bit. (2) It's already damaged. (3) In that condition, it's only worth melt value and its illegal to melt cents. Go for it.
A quick soak and thorough rinse in pure acetone (not nail polish remover) will remove a lot of (not all) organic based junk that adheres to the coin. It does not react with any metal or toning. In some cases, if the spot was on the coin for a long period of time, the rest of the coin may have toned, but the area under the spot may still be the original color, or the material may have corroded/reacted with the metal. This would cause it to have a different color As others have said, your coin has paint, nail polish, or maybe even solder (which wouldn't be removed with acetone). It is not a mint error. I wouldn't bother with trying to remove it, unless you're really curious. IMO, you're not gaining anything, it's probably more trouble than it's worth.
