I had to read that twice. I thought you posted RED cuckoo. I was about to ask where I can find red cuckoo Marans!
Maybe I could make some from cuckoo and BTB.
All I have of Ernie's Marans are white ones and Black Coppers. The copper eggs are pretty dark, but not as dark as my best line. The white ones are ok, but again, not as dark as my best line.
They are gorgeous birds, though.
FYI that book can be downloaded in the readers choice of format here:
https://archive.org/details/cu31924003158312
I've downloaded dozens of fantastic and valuable chicken books from the Internet Archives. There are hundreds of poultry titles available there.
She doesn't look like a Marans. A Marans has white skin and feathered legs. The one in the picture seems to have yellow legs (hard to tell from the pic), and no leg feathering.