3 buff orpingtons, all look alike with one diference

[marcomercer]

I have 3 buff orpingtons, They are all the same age, about the same size and featherings, these are 3 weeks old and one of them looks to be getting a waddle which is turning red while the other two are not. This is my first time at chicks So i'm still unsure of what I am doing. I al nearly positive this 3rd chick is most likely a roo. The combs all look alike, very minimal.

 

[Johnn]

Pics would be helpful!