It is my understanding from previous research and discussions here and on the SAAC Forum that somewhere around the first 200 67's that got Magstar wheels had the center area painted black. From that point forward all the Magstars used, even the over-the-counter service part wheels (early) had the dark gray appearance. From my research, the dark gray appearance is not paint but an anodized treatment of the as-casted aluminum center. To my knowledge no one has been able to successfully re-create that original anodized surface when restoring the wheels or by the companies that have reproduced this wheel. Paradise Wheel has always painted center black back when they were restoring wheels and on the wheels they manufacture. A reasonable facsimile of the center appearance can be achieved by painting the center area with a good representative color.
I have a car build the following week from yours and still have the original Magstars. They did NOT have black centers from the factory. That is the only factual data point I can provide.
I hope this is helpful. Some of the experts may have better, more detailed information to share.
Tom Gilliam
(270) 755 - 6417