If they were three months old when you got them, they would be four months old now. At four months, I think that is a female. The redder comb would mean "she" is making progress toward maturity and egg laying age.Yet another thread revive- this one is looking suspicious still. It's the only one with a tattered tail. And slightly more red than the other 2.
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Sibling for comparison. Slightly less red and less waddles.
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If the age was wrong, they are still a month older than they were before, so I think it is probably female in that case too. I would have expected a male to change more in a month, based on where they started.
(Of course I could be wrong.)