Just noticed (refer to the pics above) that the Font is different. In fact, two of my black/silver are the Pontiac font on the car, and the other two are not. The black/gold are not the Pontiac Font.
I don't recall what my spare black/silver is, or my spare silver/black for the SLE. I need to check them when I get home tonight.
Regardless, the black center caps are EXTREMELY rare and nearly impossible to find. I'm keeping them, particularly since I only have 4 of the black/gold, and no spare. If I lose even one (at high speed), the old ones have to go back on.