First of all – Welcome to the board, Nicky! I hope you'll like it here.
yes, I've heard that too, that your hair gets lighter, when your phe levels are higher… Well, and about the hair getting thinner… I could imagine, that if your not taking regularly your formula, this could be a side effect, or maybe you're taking in too little? Could this be? Do you have regular visits at your dietician or PKU doctor? How many gramms of protein supplement do you take in per day?