Unless its a rare hammer probably easier to replace it,
If your handy, like to tinker with stuff, feel like experimenting
and have an old worn hammer or trigger I have had some success on a set that the previous owner polished,
First scuff it with fine sandpaper to prep the part then apply Birchwood Casey Perma Blue paste unevenly in stages and it usually results in a close match to case coloring.
If you dont like the result you can remove it with fine sandpaper but experiment wth an old part first to get the "feel" o the stuff,