"Paint" is more to diminish "rust" than for cosmetics. Leaves usually had a misting of black on them, at least on the Chryslers we've had. Nothing shiny or anything like that, just a misting of a satin black color. It might be that some steels have a layer of oxidation which just happens to be "black" on leaf springs?
Paint protection on torsion bars can be more important than for leaf springs. I really can't think of any black paint I've seen that really duplicates the factory OEM look! Might need to start with a flatter black, then mist some satin black on top of that?
CBODY67