Have you thought of finishing the metal parts in brown instead of blue ?
Birchwood Casey has all sorts of wood and metal finishs that work well. There browning solution takes a little more work than cold blue but looks real nice on a Hawken rifle.
You need a propane torch or a way to heat the metal, then apply the solution, steel wool lightly then repeat several times until the color is deep then rinse it well and oil to prevent any further rusting.
The stock finishing can be from very simple as just sanding the wood smooth and rubbing on a couple coats of Tru Oil with your fingers or it can be very laborous such as sanding all the way to 400 grit, filling the pores of the wood, sealing, staining, and many hand rubbed coats of oil until a glass like finish is produced.
I have built several muzzleloaders and finished many others and for a hunting rifle just like to keep it simple but nice looking. The cold blue works OK but wount give deep color but might be just what you want ? Have fun with it , most anyone can end up with a nice looking rifle and at some point if you want you can always refinish it and go a little farther on the wood and metal finish. Jed