My first guess is that the leaf is infected with a virus called mosaic leaf virus. Sometimes this appears if tobacco plants or old cigarettes are nearby. My second guess is that a weather incident such as hail or a freezing rain hit the leaves. The practical solution is to wait it out and see if the new growth is infected - that would mean a virus infection. Infected plants would need to be uprooted for a fresh start. If the leaves suffer from hail or rain damage then the new growth will be healthy and you can continue to use and harvest the herbs. Keep Growing, Marianne Binetti