The color is a bit reminiscent of the color Salmon Faverolle pullets have when they begin to feather out too. It's not quite the same, but I wonder if the pattern/gene is there from the paternal side of the family. And of course who knows what the Black on the cochin is covering.
They do look very Mauve to me also, but I only have one Mauve hen and didn't breed her.
You can see her in these pictures...
Mauve would indicate Chocolate and Blue at play. Perhaps @The Moonshiner, @Amer, or @nicalandia could deduce what's going on.