Hey Jim, I struggled with this exact problem this spring when I powder-coated my rims Matt Black. You cannot powder-coat the centre caps, they must be spray painted. I tested out many. Go to a professional auto-body supply and get a professional spray paint. Under no circumstances use anything from a Walmart, Home Depot, Canadian Tire etc. I used U-POL Matt Black and it came out stunning.

The thing you have to know going in is that they will not match the wheels exactly once you're done. This is a result of the different drying times of the paint and the powder-coat, the different underlying materials (plastic vs. alloy), and the different finishes (powder-coat vs. paint).

I am really fastidious and this really bothered my eye when I was preparing them to go on the car. But once they're on the car, the different angles upon which the light hit the rims, and set against the black of the tires, everything really comes together. You will not even notice.

The one thing I would suggest though is to paint your centre caps first and then have your powder-coater match the centre caps. This will get you as close as possible. You will love the result, it really looks amazing! If you have any more questions, let me know and good luck!!

Jeff