Provided it doesn't affect visibility of the ball, I'd leave them black. I'd imagine it may reduce playfield wear and possibly extend the life of the ball. I can't see it harming anything.
I thought you could get 'carbon' composite balls at a premium price that look just like these 'protective' rubberised ones. you could explain "my kiss balls - they have protection" - just be sure not to say the first two words in the wrong order
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