By 20 weeks you should be able to determine eye color. They may be gray or greenish yet at this stage, but should not be black or very dark brown (the iris). You should also be able to pick out the birds that will have a nice green sheen on the feathers and cull those that are predominantly purple. And all the obvious things: parrot beaks, crooked keels, crooked toes, wry tails, split wings. It may take another month or two to select for wing carriage and general body conformation if the feathers are still coming in. Other things being equal, choose the heavier birds - of course \"other things\" are seldom equal. Oh - I don\'t worry if toenails are black or not. None of this is new to you I\'m sure.