My friend, the trainer at our barn, and I turned out all our horses together the other day. There was my Aires (two-year-old Percheron/paint cross), Cassie (16yo arab mare), CJ (9yo arab gelding) and Rex (10yo arab gelding). Cassie and Rex are stall neighbors and Cassie is totally head-over-heels for Rex. Keep in mind that all the boys are about the same size (right around 15.2hh) and Cassie is about 14hh on her tiptoes.
You'd *THINK* my big black and white monster would be the outcast among all the noble arabs, right? WRONG! CJ was the outcast! Cassie kept running him off whenever he'd try to go hang out with Rex (we call Rex, CJ and Aires the Three Amigos because whenever they are turned out together, they are inseparable). Aires was treated like the tag-along kid brother and basically ignored. Cassie kept charging at CJ and trying to kick at him any time he came within ten yards of the others.
So, horses don't always discriminate how we'd predict!