I think your coin is old enough to form natural toneing. It can form when coins are in storage for a long time and have been exposed to some kind of agent that makes the metal react. Like finger oils. It's very nice and I would keep it for a study piece. Abe sure has a big smile on that one. You did well to get a photo that shows the color, I have a difficult time with it.
My first thought- Experiment! My second thought- Gross, Ill pass My third thought-Well....I could.... My fourth thought- Nope
As you can tell some people dont like toned coins. I have to ask where you aquired your coin. It looks to be uncirulated by the condision of the memorial steps.