Appearance wise , stainless is more than acceptable. However when using stainless parts with threads that are “demountable” beware of the welding effect you can get making them unremovable. Engineering wise they are a nightmare. Use a non stainless nut not stainless to stainless. Blacking in the fifties was called Brunofixing. You can still purchase chemicals to blacken mild and carbon steels. The protection is mainly oil impregnation.