koren,
This solution uses the deterministic nature of truth tellers and liars and non-deterministic nature of a random answerer. For any question that has a definitive yes/no answer (e.g. "Is 1+1=2?") both truth tellers and liars can know ahead of time what their answer will be and they can either tell the truth or lie about it. However, a random answerer cannot predict his future behavior, so he cannot answer a question about his next response. Again, as bonanova said, that's based on the assumption that random first determines the true answer to the question and then decides whether to tell the truth or lie. So, if R is asked "will your second answer to this question be the same as your first answer?" he will fail to determine the truth value and show a white light.
Now, in your last post, you're suggesting that R assumes either T or L before a question is even asked and then answers the question as T or L would. That's a different behavior and will require a different solution, but R acting as T or L can still produce different answers than T or L would.
So, can you clarify the behavior of Random?