I think natural would be correct ... but it will surface rust.
Then paint is not easy, brake fluid will destroy the paint ... kind of difficult to not spill a little at some point.

I wonder how it would be to just clean it, then rub oil on it? .... to keep it from rusting.
To be fair, I painted mine. Then I replaced it with a 2 circuit MC. The paint was in really poor shape and I had not even drove it yet.