You're missing the mahogany part too. wink They're not just a gold birchen. . .
Correct, & also additional melanisers, but they are not really relevant to the thread.
I believe the Golden Cuckoo Marans are Barred Black Coppers, but I'm not completely sure about that, but either way you...
Cuckoos are basically Extended Black,Barred & Silver
BCs are Birchen,unbarred & Gold
Your cross breds will look like Cuckoos with gold leakage and will be
heterozygous Extended Black/Birchen; Barred/unbarred; Silver/gold (cockerels) & hemizygous silver
pullets.