All boas gain yellow as they age which is what turns them brown/tan. It varies per individual and per morph but in general they will all change.
Specifically looking for grey, I do agree with WrongPython that some morph locals of CA boas will probably be your best bet, but it is not going to be an easy find*
Good luck in your search
* a grey boa, we call them 'baby greys' for a reason, they only look like that when babies
Reply With Quote