Well, it would be hard to tell, both of mine change pattern a few times a day. One I believe is a male, and he's starting to get some very nice baby blue throughout the day. But a very dark top of the head could be a few different things. Post a pic so we can all see and maybe better assess the situation. A few things to remember with these guys. They don't need a heat lamp. The linear fluorescent bulbs are enough if the ambient day time temps are in the 75-78 range. Also, they require a good deal of water. We spray ours 4-5 times per day and they love it. I have a MistKing on it's way to better manage that situation.
Anyway, post a pic and we'll see if we can help.
Luis