Year old tegu with head going green

[Johelian]

Heya,
I posted this on another forum, and I thought I would share it with you guys; my year old tegu's head is slowly going green. I have no idea what has caused this, and Im asking around and looking up resources to find a reason for it, but definitely over the last two weeks his head has got more and more minty green in colour. I have a couple of new pics in the album in the gallery for anyone thats interested, but if anyone has a clue as to why this is happening I would love to hear your opinions.

Before you ask, there is nothing green in the cage that could cause it

Blue tegus start greenish. They turn tan/creame as the green goes away. They then begin to look black and white. As they become a year old they start to turn a sharp powder blue. I have not heard of a tegu turning green that late, but I am new to this. Liz.