Well, this is kinda getting into the area called the Gun Builders Bench here on the forum but to answer your question, yes, you will have to finish the barrel and the other metal parts.
How you do it is up to you but basically you can use a cold bluing, a hot browning, or a cold browning method.
The cold bluing is the stuff you get at a gun store and the results will not wear well and it (IMO) will look pretty poor.
The cold browning is perhaps the easiest and is the method used back 'in the days'.
Some forum members seem to like a soft gray finish and that is easily done with Navel Jelly.
Anyway, to really answer your question to the depth it should be answered, post it on the Gun Builders Bench.