Brunette chest mark

A brunette goes into the doctor's office for a checkup.
As she takes off her blouse, the doctor notices a red H on her chest.
How did you get that mark on your chest?How did you get that mark on your chest?, asks the doctor.
Oh, my boyfriend went to Harvard and he is so proud of it he never takes off his Harvard sweatshirt, even when we make love, the brunette replies.
A couple of days later, same situation, with another blonde. This time the doctor notices a blue Y on her chest. How did you get that mark on your chest?, he asks. Oh, my boyfriend went to Yale and he is so proud of it that he never takes off his Yale sweatshirt, even when we make love, the blonde replies. A few days later, a redhead girl comes in for a checkup.
As she takes off her blouse, he notices a green M on her chest.
Do you have a boyfriend at Michigan?, asks the doctor.
No, but I have a girlfriend at Wisconsin!