Not sure if it was said, or if you still care, but it could be variegation (I think that's re right term anyway). To my understanding, it is caused by lower concentrations of certain pigments in certain spots, and is a rather common condition in plants. I have not read of it being detremental. I have a Trainwreck going right now in flower that has way more prominent mottling than yours, and I will get a picture of it up when my lights come on in a few hours.
Cheers
