If your brakes are stock and small say 2 caliper units, paint it black or a dark silver.
If you have big brakes, then it warrents red or another color.
To me, stock, painted brakes in red, etc look silly.

The red brakes originated from Porsche, they call them "Big Reds" and they are red to show the brake upgrade.
The yellow Porsche brakes are ceramic (PCCBs) and are painted yellow and cost like $8,000 to upgrade to.