Welcome to CoinTalk! I agree with green18, it looks natural, but I think it stayed too long on whatever was toning it. The toning stages start with yellow, then gold, then orange, red, so on until it reaches black, or terminal toning, which isn't desired by many people. Something tells me that it was toned really nicely when it was still uncirculated, but then it somehow started toning again after being circulated a bit, and it started to develop a black layer over the nice toning. It's still a nice coin!
Great reply’s thanks guys and gals! I just love these old darker coins especially this one with enough detail that you can see the feathers and the Eagles eye too!