Is this a copper pigtail?

Enough about toilets for me because that sucker is down and out, lol. Since the bathroom being redone is mainly used by the kids I was going to pigtail in copper to the outlet and install a gfci receptacle. When I pulled out the old receptacle it was hooked up to a pigtail already and the color of the solid wire was copper. Nothing I have read shows aluminum being any color besides silver. I used the exisint connections and the outlet works fine. Any input appreciated as usual.