Regardless of what color it was when it went on the factory assembly manual says that area was to be sprayed black on the assembly line along with the rear end etc. There is documentation that can back you up on that and none I have ever seen that can say it was natural. No idea how they were colored when they were installed. Last NOS bar I bought came satin black but again that is no indication how they came on the assembly line back in the day. Bottom line is black is your best bet.
All I know is that the orig on my GS was a faded black (over the years). I repainted semi-glass black. We had to use a cutting torch to remove some of the old bolts.