Are those lines embossed or are they actual louvers? They remind of a design that Harry Bradley did in one of his drawings, that I reproduced in Photoshop.
Just enough venting to cool the brakes.
Why black? They will disappear. Maybe body color? I got a set of wheels I'm going to 'paint', but the plan is satin black powder-coat (to conserve them, they're semi-rare Marathon wheels) top-coated with Real Aluminum Plastidip with a Pearlizer top coat. I'm hoping for a finish like you see on high-end aftermarket wheels, on steelies.