If it helps, mine has the brass escutcheon's and black screw (flat head type).
The picture you show where it looks like the screw is stainless, may just be lighting. I held mine up and depending on the angle of the light, the black screw looked shiny like stainless.
Thanks very much. Here is the email Walther sent me regarding the aforesaid.
"I don't know where Altamont got their rosettes or screws or washers.
You could contact Altamont and ask them, i'm assuming they outsourced those as well.
But all that i can say is that we have a single type of screw for the PPK and PPK/S.
The PPK and PPK/S has been manufactured by several different companies, and imported by several different companies.
So that explains why the grip screw, rosette, and washer look different depending on which type of gun.
Interarms and Smith & Wesson both had several limited edition versions of these guns, so there may be brass screws, or stainless screws.
The modern production grip screws are the only ones we have, they are a black anodized steel screw".