A dark heat treated cast iron with multiple bright fresh machined surfaces. Don't know any paint that could replicate both of the finishes and if you did you have the issue of cracking/damaging the paint during install and rusting.
Digital camera settings and well as your monitor settings may make this picture appear different than it does in person but you get the idea
If you have to paint my might get by with one of the dark ceramic charcoals on the non-machined surfaces than after adding them a coat of protective oil just like you would if you were restoring the spindle