They were natural. I lightly phosphate and oil the ones I reuse. The factory stud plate, C1VV-5B236-C uses lead point (aka dog point) 3/8x2.0 studs. There are a couple of reproductions that use 5/16-8 standard tip studs. Avoid them. I don't know if the stud plate under the seat on the inside is coated or not. It may get a shot of sealer after installation. The studs thru the body are sealed with calk (strip calk will work).
The retaining screw, 51866-S8 (52735-S8 what I found in mine) and the nuts, 373403-S8, or 374380-S8, or 376424-S7 to the bracket are clear zinc plated.
Jim