Do you want attention to be drawn to them or your wheels?
Black for the stealth stopping power and no one noticing them.
All other colors for police diagnostic fees. They pull you over to give you a ticket aka diagnostic fee.
Dont go ricer colors (lime green, really light purple, electric blue etc..)
I just painted my calipers last night. Gloss black. Unless you have a big brake kit there's not much point in having a "look at me" color on your calipers.
I took my rotors off cuz I painted the hats of the rotors black.
Then left the rotors off and bolted the calipers back to the brackets and covered the wheels well with news paper.
I tried to get as far back as I could on the calipers but if you look far enough in, you can see where the paint fades. Nbd to me though, nobody can see in there.