This is a subject of much discussion and I'll try to give a summary or consensus, which would apply to locks, barrels, trigger plates, etc. In general, browning or bluing are protective finishes and were not done to "hide the shine". That's gun writer myth spun in the 1950's and 1960's. Shine was considered good especially for the military. Spit and polish, look impressive, glint in the sunlight like polished steel ready to kill.
One problem in answering the question is that especially on American arms before 1800, there is often little original finish. A gun finished bright might look browned now, etc.
Most original lockplates were case-hardened, which we only see on factory guns today, more's the pity. Then any additional finish was applied if "case-hardening colors" was not the desired look.
Most folks agree that before about 1760 or 1770, iron on guns was generally finished "bright" with some barrels being "fire blued". Browning as a finish first appears in advertisements around 1770 or so. However, the finish applied to the barrel may not always match that on the lock.
Many builders choose to brown locks nowadays because they get a good acceptable finish with very little work. Current locks require 4-10 hours of hand work to polish to a bright finish without rounding over edges, dishing plates, etc. because they are cast and have surface pits. It must have been much more laborious when locks were forged, and there is evidence this work was farmed out to child labor in Europe. Most customers would not want to pay a decent wage for that type of work.
In the last 10-15 years many makers have also been turning to "patina" finishes, that simulate an aged appearance. Locks and barrels etc do not have a uniform color or smoothness and look like a well-used gun.
