That looks like a very nice Roller! The backsight is correctly mounted, even if it looks a bit odd. See Layman, Remington Rolling Block Military Rifles of the World, pp71-73. And yes, the middle band does seem to be reversed. Butlersrangers has made the correct comments about ammo. And the receiver is not color-case-hardened. What you see is patina from handling.
If the bore is OK and there is no nasty slop in the action from worn pins (see my previous post), then you may well have a keeper.