I understand these Porsche fasteners use a dip-spun applied zinc-aluminum coating called Dacromet, but the current name for the more environmentally-friendly version of it is called Geomet. The dacromet/geomet coating alone looks kind of matte silvery in appearance, (like aluminum) and you will see this below the green coating, if you ever have "cleaned" grease or oils off your fasteners with an aggressive solvent cleaner, (like brake parts cleaner - or anything with acetone on it, will remove that green coating very quickly.) Solvents will not touch the base Dacromet (aluminum/zinc), however.
Based on the following reference, which says [Porsche-spec'ed geomet] "sealers include ... pigmented ... green for identification purposes", we might infer this solvent-removable green topcoating to be an "Inorganic silicate sealer topcoat", which "provide[s] consistent torque tension values and additional corrosion protection."
http://michiganmetalcoatings.com/yahoo_site_admin/assets/docs/Geomet_Brochure.28482815.pdf
In my experience, it's still a good idea to clean older dacromet fasteners before re-using, and also apply anti-seize, ideally. The commonly available, gray (I think zinc-based) anti-seize seems to play very well with the dacromet fasteners when applied thinly and evenly on the threads, and doing this will also help keep water from corroding aluminum whenever these fasteners are ever threaded directly into aluminum.