I just had a look at mine from a 10/70 which are still tagged in a baggie. They are the standard flat black oxide finish. I tried to remove some of the finish to reveal what you describe, but couldn't.

I agree with Ron, they have the black oxide finish, just like the four oval head, countersunk machine screws that fasten the heater control panel to the dash. Just as a point of interest that I have noticed, the four screws that fasten the front edge of the cowl panel are, also, black oxide oval phillips head self tapping screws. I often see these replaced on cars by chrome or clear zinc screws that have heads that are also too small.

Dan

I was just thinking about the volour of the heater panel screws ( on my 280Z.) I was going to paint them the same colour as the dash cap so they will blend in.

Wood screws, sheet-metal screws; same thing to me. It's basically a #8 or #10 flathead phillips screw.

Nope, wood screws don't always have threads all the way to the head, but sheet metal screws do. Very different.