It's worth whatever someone is willing to pay. I've drooled over that gun (admiring only) ever since Amarillo Mike showed it to me. IMO the gun is priced about double what would readily move in the market.
Utah, Amrillo Mike owned a spectacular Premier Imperial with full oak leaf engraving. Gone now but it was a wonder to behold.
I believe the barrel finish is original to the gun even though it is dark. One of the posters above is correct, they often did a black and white type. Also, some finishes tend to darken over time.