Copper on wings determine sex on a Marans?

[suliah]

I've got a BCM and a couple of blue marans... I've never seen brown on the heads of marans as chicks.

I do know that the black sometimes get the copper bleedthrough, and it's not good, there's a term for it that I can't remember. But the brown/red on the face has me baffled.

 

[sideWing]

Coming along nicely now. Two Roos and two pullets I think. And definitly blue.