Rob,
Yes the rim on all the flywheel clutch models would be electroplated. From about 1930 onwards, Douglas would have been using chrome. First on the more expensive models and then on the lightweights as old stocks were used up.
The center recess on your Aero would be painted black, as well as the bits of tin for housing and adjusting the clutch springs. The next bright bit would be the adjuster nut for the clutch springs. The flywheel nut just seemed to have a dull nickel plate finish.
The flywheel might have gone to rust, and painting was the only option to deal with the pitting. Or it might have just been a cost saving measure, aerosol-chrome!
I have had a few flywheels plated. Make sure they understand they only need to polish the rim, which should save money. Also, plating buildup on the hub can mess up the fit of the clutch throw-out sleeve. The electroplating is attracted and builds up faster on external corner/edges. Often the hub is a sloppy fit anyway, so I will not bother to mask the hub. Instead after plating i turn the hub and press on a bronze sleeve. This I turn to fit the clutch sleeve (giving the latter a light hone if needed to true it up.) Sloppy sleeves promote clutch-drag.
-Doug
