Yes, for sexing day-olds.
I was thinking, though, of adult drakes, whose bills and feet are yellow, compared with hens, who are black/black. Please do correct me if I'm wrong.
Mine are at 6 weeks at this point, and it's still not certain if I have 2 or 3 drakes out of my batch of 10. I'll be processing a few here in a couple weeks, and am only keeping one drake.
Oh, that's correct, haha. Sorry for the misunderstanding.