What locality is it? I have a large 9 month old male ambanja that is very slow to color up. He only colors up once in a great while and is usually just brown. It can take them a long time to color up sometimes. Im not really good at sexing them by tails unless it is very obvious, so I'm not gonna try and guess off of that. See if it colors up a couple hours after lights out. Maybe the pjs will give you a clue.