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Red gears are faster, and will give you better throttle response, but the silver ones clearly make for a more stable drivetrain at higher RPMs, which is why I would only install sivler gears.
I'd paint them white if I were going to paint them.
I have one silver, one black (unorthodox) that I will never use. The silver one has a drilled/tapped hole in it for a sensor trigger. Might be too ugly for you- but far from rice.