Gayle King is of the same skin tone as he is, so I doubt she would be so much given to believing such stereotypes when they wouldn't apply in her case.
I'm not sure where Liberal lines come in or if that applies to the nine other jurors. If 9 of them are thinking a certain way, and they assume the 10th must be thinking along the same lines, I'm not sure how or why racial stereotypes would be a factor when what they're assuming is something they're assuming to not be bound by race.