dabac

I can't think of any way to make it black where result would be worth the effort.
Well, possibly the marker.
But last time I checked, there were still ceramic coated rims available.
They're expensive, but unless you hit potholes, or jam the wheel into a bike rack etc (which can cause chipping) they'll last for ages.
The brake tracks on those are kinda black. Or a dark graphite gray.
You'd have to have the wheels rebuilt around those, or have them built up as a new wheel set.
You can keep the brakes, although new, ceramic-specific pads are recommended.
Braking would be improved, particularly in the wet.

Ceramic coating is sometimes applied to piston heads on high-preformance engines. If I had any pals in that line of business, it'd be interesting to know if an existing wheel could be "upgraded" to ceramic brake tracks.