Yeah it's the coloring and body shape. And you can tell what sex they are when there voice changes in a few weeks. The females will quack and the males will make a hissing noise.
Oh the big one is the one being picked on!? That must be a little cute! Hopefully they will stop soon. You could distracting them with a stuffed animal or something.
Uh oh, the eye pecking. I don't think they'll do that for long. Have you fed them yet? Usually after I feed them they quite. Also he might be trying to preen them. I didn't think about khaki's. They look like those to!