I did the same thing with 2 different Rustoleum paints.
1. High Perf. Wheel Paint in their Custom shop line (248930 Graphite)
2. Metallic line of paint (7271 Silver Metallic)

While neither is the exact right color, spraying down a base with the silver metallic and then fogging with the Graphite, created a near perfect match to the mint pair of 71 Dark Argent Centers I have.

Nice thing with doing this is you can make it lighter/darker just my fogging the part with a little more/less of the darker color.