Just as the title says. Why should I struggle to figure out which pet belongs to who? My guildmate's horses will look grey to me. Or blue. I have to sit and figure out who a pet is attacking to know if it belongs to a guildmate or the guys trying to kill me. In big battles it causes things to become unnecessarily chaotic. In mounted battles I have to target a player to know if I should be attacking their mount. It's something that gets messy the more players there are on the field. Nothing sucks more than accidentally helping to kill your friend's mount because you had no way of knowing what you were hitting. Guildmates' pets should have a green name. It shouldn't be gray to me. It shouldn't be blue either. It's simple.
