Their combs, especially the partially white one, are quite red for that young. Also, the coloring. The black and white one has the coloring of a male. If a female were black and white, she'd be patterned differently in that most of the white would be up front, most of the black would be towards the rear, and there wouldn't be such a definite bordering of black on the neck, white on the shoulders, etc. Notice how the black seems to group mainly around the neck, tail, and wing feathers? That's a boy thing. Also, the black on the chest is another boy thing. It is hard to explain, but he's a duckwing with dominant white leaking in. If he were pure duckwing, he'd show what I mean, by how the shoulders become a definite silver/white or golden/red color, the chest goes solid black, and the tail/back/neck feathers go solid black, then get some golden or silver in them as he matures.
It is hard to explain, really. When he matures a little more I could explain it better, it's just, if you understand certain color patterns, you can catch them early in development and see what gender the bird is. (This only applies, though, for duckwing, wheaten, and birchen base colored chickens)