you can also get a paint pen from Sharpie,,,,,they are filled with Acrylic paint
you might have to experiment with cutting the tip more to your liking, though,,,,,,,,,they cut easily with a hobby knife into a sharp point if that is what you want
I cut the tip on a red one from a set of five that the Lady bought me,,,,,,,I cut it so that it has a large flat surface,,,,,,,it works better for Navy gear door edges than a regular Sharpie with ink, and better than a fine brush full of Red paint,,,,,flat for large areas, needle point for going around corners
so, you should be able to cut a Black one to do what you want
Rex