On another thread I noticed some questions about how the 1907-'08 model Harley-Davidsons were finished. Going thru some files last night produced photocopies of original Harley literature. Material that probably didn't get into the "At the Creation" book on early Harleys and that may shed light on the matter. These are EXACT QUOTES:
From: 1907 Harley-Davidson Catalog
"The machines are finished in black or Renault gray. All bright parts are nickel plated. The engine casing, which is of aluminum, is buffed and highly finished and will not tarnish or become dulled in appearance."
From: 1908 Harley-Davidson Catalog
"All machines are finished in Renault gray with carmine striping, or in piano finish black, and all bright parts are heavily nickeled over copper. The aluminum casing is highly polished, adding greatly to the general appearance of the machine."
Notice here that the 1908 model was still offered in black. That's interesting. Also note the terms "buffed and highly finished" and "highly polished" when referring to aluminum crankcases. That is still somewhat open to interpretation, but clearly they were attempting to make these bikes look pretty.
Hope this helps.