According to Don Stith, Phil Sanders, the guys at the old GRRW, and a few others I have talked with over the years who have taken original Hawkens apart, the barrels were blued, most likely rust blued (a technique that goes back at least to the late 1700's), breeches and locks were case hardened albeit seldom color cased but rather a more "French Gray" color, as was the rest of the iron hardware - on full-stocks this includes: the buttplate, trigger guards, rod thimbles, etc. On halfstocks the rod thimbles were blued along with the barrels.
Just a note - while we tend to think of the fittings as iron, they were in the 1830 period were usually listed as steel fittings not iron even though they were cased iron - most likely due to the fact that they were case hardened