Well no one else has replied, so I feel inclined to say, at least in my experience, charcoal blue is more of an 1840/60 finish. And again, in my experience relatively rare on a Kentucky rifle. I owned one with a good bit of charcoal blue remaining on the barrel, signed WW, and probably made about 1850, out of the 50 or so rifles I've owned since 1980. And currently I have a original percussion Hawk rifle with what looks like might have been charcoal blue on the barrel.
By rust blue, if you mean doing a rust brown then boiling it to turn the color black, I haven't seen that either.
The underside of the barrel being uncolored is correct as is the inside of the barrel channel, but at this point in time, both areas are going to have some color/rust/staining.
As for the top surfaces of the barrel, it's hard to say what was there originally, as almost all have varying degrees of brown now. From what I've seen on the guns I've had apart, and that would be a considerable number, I think the gun left the maker with either a light rust brown or maybe a darkish French grey on the iron.
Lock plates seem to be generally case hardened grey, but from what I see not to a bright luster, more of a dull grey. Or a light rust brown finish. Remember for the most part these old guys were hunters, and then as now, a bright shiny thing isn't going to help with procuring dinner. Although it was great for the military to show off and try to frighten the enemy, or deer, or squirrels!
Just my 2 bits,
John