CF rims are fairly black. And braking isn't horribly sucky with the right pads.
If I was struck with an uncontrollable urge to build an all-black, rim brake wheel, That's probably what Id use.
Ceramic coated rims are nice. Mine are also fairly black. "Graphite" might come close. Unless you flake the coating off by denting the rim, their expected life seems indefinite. I've got at least 30.000 miles in my Mavics, with no end in sight. They've gotten a bit shinier though.
A bit expensive perhaps.
Powder coat doesn't hold up long on brake tracks.
While it does, braking sucks.
And there's a good chance that the brake track will become discolored, negating the purpose of the coated track in the first place.