I never bothered with the wing sexing because by the time I do my first evaluation they're 8-9 weeks old and I can tell at a glance. It does require the fast feathering gene which I'm pretty sure Langshans don't have but I could easily be wrong.
Edit: The hazards of posting at work, I don't get everything in there. Just to be clear, they're still white even though they have the silver gene. No such thing as a silver langshan. Anyway, and again keep in mind my genetics are rusty, but if you got one that means both the black parents must be carriers, which the old Punnett square tells me means 25% of the chicks would be white. 50% of them would be Black but carrying white, and 25% would be Black with no white. No cosmetic difference in the Black chicks. Just remember, sometimes Punnett can be a jerk. LOL
Edit 2: Was reading another breed thread and apparently someone in it was getting blue hatch out of all black parent stock. I do not know how this would be possible. But it makes me curious, keep us all updated on this little chick?
Edit 3: Because I don't want to double post, just took first step to finally getting Langshans back on the farm here, got some hatching eggs shipped in and none broke so now begins the wait to see if I can get any to hatch!