Emerald Tree Boa skin discolaration.

Hey, guys. Thanks in advance for your time. I have an Emerald Tree Boa who is about 16 months old. I've had him since he was 4 months. I wanted to get an opinion on the black scuff in this picture. Because of his skin color, finding something compatible has been really hard. Since ETBs are comparatively rare in the pet trade, not a lot of pictures like this exist. I would have just taken him out and soaked/wiped him a bit to see if any came off, but ... well ... he's a jerk. Ever since that time I had to remove shed from his head. I don't mind the bites, but I don't want to stress him out too much.

I'll try to give details that might be relevant ... I haven't seen any of the black spots moving. That is, they don't change position. They're in the same place every day. He is on coco husk bedding. He is eating regularly (2 weeks apart, large pinky rats). He follows the same routine every day. Lights on, hide behind the tree. Lights off, dangle from the lowest perch. He'll drink a bit of water from the bowl, but doesn't soak.

The heat stays between 78 and 81, with humidity slowly swaying between 55-85 over the course of a few days. The cage is an Exo Terra with plexiglass air-tight sealed on top and a 46w heat panel installed. Admittedly, the air flow isn't the greatest, but I felt I had to sacrifice some of that to keep the heat/humidity where it should be.

Anyway, thanks for your time again. Here's a picture -
http://s24.postimg.org/j5y7gablh/20151012_114618.jpg