According to ITTF rules, both sides of the racket must be black and red. This is because there are too many kinds of rubber, including granular rubber (positive rubber, long rubber, raw rubber) and reverse rubber (flat rubber), each of which can make the ball rotate differently. And if you don't distinguish them, they are all black, then you can't distinguish what kind of rubber your opponent uses in the game, and you can't distinguish the opponent's ball path and rotation. In this way, the opposing sides can know what kind of rubber they use when hitting the ball through color discrimination, so as to achieve the purpose of fair play.