Flat black only helps radiative heat transfer. Since the paint would be a coating on the aluminim, it will slightly inhibit conductive heat transfer because it forms an insulating layer.

(It's noteworthy that "radiator" is a misnomer for the gizmo that discharges waste heat since it doesn't really radiate anything significant.)

But the effect of enhanced radiation or reduced conduction would be tiny at the temperature deltas involved, so the biggest impact of painting would be visual.

How about metallic orange with pink racing stripes?
--
Don Foster (near Cape Cod, MA)