Classical Pinup Bodyshape
Pinup clothes form the Curvy section are based on Classical Pinup meshes created by Warlokk.
Classical Pinup is a separate bodyshape and it has its own showerproof nude mesh and nude skintone which can be found here Also find tons of skintones in this forum. (You have to be over 18 and registered/logged in to view this page).
This is a bodyshape created by Marvine at Insimenator.net
If you want your Athletic Sims to keep their shape when nude you have to download her base meshes and showeproof Barbie skintones here.
Anatomically correct showerproof skintones can be found here. (You must get the base meshes anyway)