Hi,
nice looking GTP
They can calm down in time with regular handling , but like all animals !! they each have their own attitudes.. some tame down while other may never..
the fact that once out of the cage he seems to be alright is a good sign..
to avoid bites, the best way to get it out of the cage , is by using a snake hook to get him moving and guided out.. or a removable perch that you slowly tilt to get him moving..
then always go from behind to hold it as it moves around .
once awake and on your arm, they often like the warmth and will perch ..then again some never stop exploring
the Biaks have been known to be more of a nippy locality
as for color, they can take up to 5 years sometimes before turning completely green.
they usually do unless you paid the big $$$ for a designer breed of high yellow.
for additional info regarding high yellows, as mentioned above !! they can take years before they fully change, so unless a seller has paper work backing the GTP, be careful when buying a said high yellow GTP, many claim high yellows or canary to get $$ to have the buyer stuck with a green snake two years later

nothing wrong with a green GTP, hell that's what they are all about.. but when you pay thousands and end up with a 300$ GTP
back on topic
yes in time he should calm down with regular handling and they aren't as bad as the reputation they have :-D
just respect him and go slowly avoiding all movement from the front, if it coils up in the S fashion , stop moving and take your time..
if it bites and doesn't let go, use a spray bottle with water to get him to let go..
even having a little vinegar mixed in the water helps and won't cause any harm to the snake.. the smell and taste will get him to let go. but very little, like a 5% mix , but this isn't usually required, only with nasty ones that tend to bite and not let go..
congrats on your first GTP, looking forward to seeing the others you will get hehehehe