I could be wrong here, but my guess is that it is unpainted. The SDs early QDs were unpainted and were also a dark gray in appearance. See the picture of the powerhead of my SD-20 below.
-Ben
I agree with Ben, all of those early models had unpainted powerheads from the factory. I have a couple RD Johnson Big Twins,
as well as some early Qd motors that are that way. I also have an early Evinrude Light Twin from 1953 that appears to have never been painted, as in bare aluminum.