Black or silver here.
I painted mine silver, since I just hate rust, I have done it to pretty much every car that I have own ( besides my EVO X which has brembos )
For me the heat dissipation is not an issue since I'm using the car as a DD,
but even if I would used it at the track.... this is a high temp paint,in the worst case it will discolor a bit ( darker grey ) so it would look just like original stock brakes. When it comes to heat at the brake system level, the vast majority of the heat goes to the rotor, then the pads, next in line is the piston in the caliper, then fluid. That is why when it ( fluid ) is being changed mechanics know what sort of a driver " takes care of the car " The more heat the more black overheated fluid, time will do its thing too.... but it is a separate issue altogether .
So yeah ! silver for me please !