Go to the part where Joey first see's the "hot girl" in Ross's building. When he goes over to find her he ends up at Ross's apartment because he miscounted. When he goes to knock on Ross's door he is wearing a purplish shirt and he has one arm up at the top of the door frame. When Ross opens the door Joey's arm is down and the bigger problem, he is wearing a Black pull-over sweater. Then when he leaves he is wearing the purple shirt again.