I think you need to wait a little longer to see for sure. If the white is larger then the others and the same age then it's safe to assume it's a roo. Hard to tell with the others ones though since a lot of there feathers haven't came in.
I have a three week old silkie that throws her leg when she walks or runs. She had no other signs but this and it just started about 5 days ago or at least to the point I noticed it. She is also missing a toe on each foot and I'm wondering if that had something to do with it. Any ideas???