Not a buff orpington?

[Boothschickfarm]

Bought what I thouugt were supposed three little BO. but as they started to feather out one of them doesn't look like their sisters. Here's a pic of them, the one I'm wondering about is the little white one. Different breed? Roo? They are 4 weeks old. Your the experts!

 

[sourland]

The white chick is not a buff orpington - it almost looks to be some sort of bantam.