Parkerized parts were used extensively on old Harleys. Basically, the raw, beaded steel parts are soaked for a period of time in heated oil, then removed and baked again. Its basically a burnt on oil finish. Its really greenish brown, not black. I could copy the recipe from a Harley restoration book if someone's really interested; do it in your oven (when the wifes not around) or on a hotplate.
Ted, my other 2 bikes are Harleys
Beautifull, sunny Berkeley