Unusual Lionel Wheel Cups (for rivet press)

I recently purchased a rivet press outfit with an assortment of wheel cups for Postwar Lionel locomotives. It is not an outfit that was sold by Lionel, rather it has an assortment of pieces, including some by Chicago Rivet, and some unknown.
My question is about the wheel cups.
They look to be a very good match as far as machining goes. They look to have been made the same way as cups that I know were sold by Lionel. But the color / finish of the metal is different. At first I thought they might be aluminum, but they are attracted to a magnet.
I have two pictures below.
The lighter colored ones on the right are the odd ones.

Anybody know anything about these cups?