For the concours enthusiast, this question comes up fairly often. What is the correct paint color for the MGA wiper motor? And the answer is, it varies some. In general, the cast gearbox housing and motor end plates would be left as natural casting finish. The gearbox cover and parking commutator cover and all fasteners would be zinc plated. The two-piece base mounting bracket would be painted chassis black.
The motor housing should be painted, but this is the part that varies with time. Some people think the motor housing was never painted, likely left to rust with time, but this is or was probably never the case. Some mid production parts were apparently painted with a thin coat of mat black, which was prone to peeling off to leave a nearly bare and slightly rusted surface with time, giving the appearance of never having been painted.
Post-war cars up to 1955 (Y-type and T-type cars) seem to have had black wrinkle finish paint on wiper motors. This may have carried over for a few very early production MGA, but most people would never see one of those. There was a sectioned Twin Cam assembled for auto show use that was sporting a wiper motor with wrinkle black paint, but that may have been a one-off for the show car only.
Almost all British cars from 1955 to around 1961 have mat black finish, cheap thin paint with no primer prone to peel off, which is often interpreted as no paint. Late production parts from around 1961 on would have silver gray hammer-tone paint, commonly called "Hammerite" (although Hammerite is a brand name, not a color code).
The external interconnecting wire for parking commutator was usually red, sometimes interpreted as brown when aged. Although I have seen some that are red with a blue stripe, which makes sense since this wire is switched to ground through the parking commutator.