Power Brake Booster! Black or Plated?

My '70 Swinger has narrow, black booster (as OEM) but all my other (A and E) vehicles had the wider (Midland-Ross) plated booster. I have seen a few of these (M-R) units painted black but I suspect it was owners' choice - - since other pieces (such as wiper motors, module brackets etc.) also black.
Those resto books usually have this info but my Challenger/Barracuda (E-body) book (by Paul Herd) currently loaned out.