Mallard duckling question

[Luv Ducks]

I have four Mallard ducklings that I am selling out of the six that I have left. They are only 4 and a half weeks old but I can see a green sheen on 4 of them. I want to keep them all sexed together as that would be safest for a small flock. If you can see a hint of green on their heads wouldn't that mean they are drakes? I would think so but am not sure. The other two do not have the green hint so I am keeping them. If anyone knows this please respond, thank you.

 

[fatty and friends]

if you send pictures (and videos of their voice) maybe we can help you, but both my girls had greenish heads as teenagers that went away after they grew up

 

[Luv Ducks]

if you send pictures (and videos of their voice) maybe we can help you, but both my girls had greenish heads as teenagers that went away after they grew up

Thanks, I don't know how to do any of the high tech stuff so I guess time will tell. I appreciate your answer though. Thanks again.

 

[Luv Ducks]

One that I kept is a real little quacker already so I am sure it is a female. The other one is darker than all of the rest and bigger so I was hoping it was a Rouen since I have two Rouen hens and 3 mallard hens. The nest had 19 eggs and 11 hatched and it was a mixed bag of the two but mostly mallard. The little quacker had no green on it at all and that was what made me think the others having the green were all males. I appreciated your opinion though so thanks again for answering.