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Blue copper x blue copper will produce black copper, blue copper, and splash copper offspring on average.
Silver/gold is a sex-linked gene, so hens can only have one copy of the gene. Therefore, a blue copper hen can't be carrying silver. If she came from a blue "birchen" roo, then that "birchen" roo was actually heterozygous -- carrying one copy of gold and one copy of silver. But the hen has to be one or the other (gold = blue copper, or silver = blue birchen). If a blue copper hen is mated with a true birchen roo (two copies of silver -- no gold), then they will produce blue "birchen" male offspring that are actually split silver/gold, and blue birchen female offspring.
Everybody needs to remember that ALL "black copper" Marans have the birchen trait, since the black copper pattern is BASED on birchen (ER). The main difference between black copper and birchen birds is the presence of silver or gold. And a lot of "birchen" birds are carrying gold, so there's a lot of mixed flocks out there!