Okay so why would you ask if Orange is a girl but not why Blue is a guy? Humans have to have genders and Orange conveys a very feminine attitude. And valve has plenty of female characters lol Portal was basically all females before Portal 2.
The idea that they're both males doesn't make sense to me because VALVe said one is masculine and the other is feminine. also i could have typed a lot, lot more. and yes their robot appearances will always be tops.