confusing duckling

[KaziCritter]

I have a pair of rouen ducklings I got at the local feed store. They are almost 2 months old and both are nearly fully feathered, just a bit of their necks, heads, and flight feathers on their wings to go. They have identical coloration (feathers, feet, and bill except one spot mentioned below) and both are transitioning from from squeeky chirp to quack. They only quack about 1/4-1/3 of the time but both are loud and sound just like the previous girls I've raised, the quacks are loud and clear with no rasping or anything. Now here is the confusing part, the new feathers on their heads dont match. One is getting the expected browns but the other is getting the typical male green ones. Is it just a confused duckling or can a male have an actual quack or a female get male coloration? I can't figure out what's going on with this one, my only adult rouen drake hatched with his neck band (or at least had it when i got him at a few days old) and didn't match the coloration of the rouen hen he was raised with after they started feathering.