I cannot locate it again to save my hide, but I saw in one of the longrifle books a photo of a late 18th century gunsmith advertisement from Wilmington, NC.
The gunsmith advertised various tasks like flintlock repairs, door lock repairs, etc. He also advertised that he wanted top quality curly maple and would pay well for it. Trust me, there is very little sugar maple in balmy Wilmington.
The period ad also advertised both blue metal inishing and brown metal finishing. That answered in my mind whether either finish was more appropriate for the time period of our interest. I'd say "both".
God Bless, Marc