Factory color of rear license plate holder/bracket?

[russgoodman]

I bought a custom sheetmetal box license plate holder for my 69 fleetside that raises the license plate up even with the bottom of the bumper. I wanted to powdercoat it so it kinda looks factory correct. I see all of the repro brackets are black, but somewhere I thought I saw that from factory they were argent or silver. This is the part that bolts into the center of the fleetside rear bumper and has the lamp housing for the tag. Anybody know what color they were originally? I was going to hit it with satin black, but before I do I wanted to see what you all thought. Pic of what I'm talking about