If you are inquirering about the color difference on the obverse, I will say not an error. It is toning from contact with some chemical. Poor Garfield, sworn in March 4th, Shot July 2nd, Died Sept 19th. 1881.
Even worse, he may well have survived the gunshot wound but died as a result of the surgeons trying to remove the bullet. I agree about the color, BTW.
