To answer my own question, I would say that in all likelihood, I would root for Kobe.
As others have said, it's the name on the front that matters most, however, at times we do have players we become attached to, or at least favor.
I think if Kobe was in green, we'd be a little more lenient with him on the way he carries himself, as well as some of his actions on and off the court.
Likewise, there would probably be some of us who would get ticked off at KG for his trash talking, saying that the guy needs to cool it, if he were playing for, say, the Miami Heat or LA Lakers.
Point being, if Kobe was in Celtics green, he would still be considered a jerk, but as Roy said, he'd be "our jerk."