Two designers that have already won a Red Dot concept design award for the Bevel Cup, Gao Fenglin & Zhou Buyi, have come together again on an idea called the Discolor Tyre. 
     Understanding it couldn't be simpler: A layer of colored rubber beneath the black casing will appear when the outer thread depth falls beneath a certain amount, as the tires become orange. Simple and efficient. 

      Fenglin and Buyi estimate that 20,000 kilometers of driving, or about 12,400 miles, will cause the colored tread to show, but there's no reason why harder rubber compounds couldn't increase that number. Additionally in countries where roads are slippery, tires could get hardened without decreasing their thread depth, due to heat or sun. A side benefit is that it would also quickly reveal tears in the casing and the sources of leaks. 
      Of course nowadays , tire manufacturers place small indicators that become visible when the tire wears down, but it's not easy to a novice rider to see these indicators, since they are tire-black as well. Rider is required to get down and inspect the tire, not very user friendly. The new system makes the inspection easier and quicker. 

      Of course, it also means that the cops can quickly tell if the tires need to be replaced. The inventors already won a few design awards, now all they need is the tire manufacturers to pick up their patent.