Gracious... not a stain, folks. That's an improper alloy mix. Happened frequently with this series as well as Indians and early Lincolns.
Nice coin. NGC, to me anyways, has been undergrading copper recently. I think the slab says MS64. Personally, I'd call it a 65.
Nice luster and a pretty good strike for the 1857. Were it not for the mark above the bow, I'd be all over it in a 65 holder. I think it's a 64+.