Okay, I Too, have pulled my supercharger apart. It has the Epoxy Coating, which, is that blunt grey colour.
My rotors look alot like yours, missing some of the epoxy coating, it wears off over time im sure, and at 139,900 kms..it is..on my car..
The Rotors are highly polished beneath that Epoxy coating, I can tell you this because I pulled apart my M62 Gen 2 (no epoxy from factory on Gen 2) Heres what It looks like
Left Lobe was washed and has 0 Epoxy coating on it, it never did.
These are the rotors out of my 97'* M90
Lightly cleaned with citrus.
What you are looking at on yours is indeed aluminum,however, its got some crap and fragments of epoxy cooked onto its surface,Thats all thats under the epoxy, nothing else.
Damien-they don't make them like this anymore
97 SSEi. 3.2mps,msd,optima,1.9 YTs,245 RE750s,SLP Headers,custom ported SC inlet/outlet, 180 deg, INTENSE pcm,42.5#injectors,255lph pump,custom soilid motor mount, 3.0 mps(maybe), and the nut behind the wheel.