Every now and then, the Rule Makers create a rule to be clear and simple for EVERYONE to understand, and straightfowrawd to enforce. Uniform Adornments is a prime example; rather than itenize 10,000 allowable items they stated 2 permissable items (a specific sweatband & defined towel).
Mouthpieces of any color combination known or imagined, with the very specific exceptions of pure white or clear are allowable, making the rule understandable and clear to any and all players, parents, coaches and even mouthpiece manufacturers. Makes you wonder how, and perhaps why, such a problem even happens. When that rule was added the notion was that eliminating white and clear mouthpieces would be a simple, standard way of determining whether or not a player was wearing a mouthpiece IF AND WHEN A QUESTION AROSE ABOUT ONE BEING PRESENT.
Sometimes it's just as easy, and practical, to follow a simple rule as it is to resist one.