I got these buff/black japanese from Cackle in a straight run with 3 breeds, if I am guessing correctly I have 10 roos. big problem as I want to keep all of them.
They are 3 weeks today one is coloring up and has lots of feathers, the other is still mostly yellow and not nearly as feathered
3 weeks may be a little young yet to start sexing them. Let them grow a little more before you panic. The best picture for sexing chicks is a good clear shot of the combs.