Basically he was saying that instead of the extended black genes making a bird solid black that it may take some other genes to make them completely black.Your over my head now!? Not sure how I would go about doing that... I have a splash roo, a black hen and 2 barred hens, a partridge roo and 3 silverlaced hens. Don't see any white or fade on that black one, she is dark as night. I think I have read that solid black and solid white can hide a lot of color genes? Like the box of chocolates, you never know what you might get....
I'm following what he's thinking and could see that being possible. IMO if its true and you had birds missing some or the genes responsible for that then the leakage would be in hackles and maybe back and saddles. That's gonna have the birchen look if you could selective breed for the most leakage. Which in this theory would be breeding towards the birds that are missing the other gene (genes) responsible for the incomplete black.
Basically same idea of breeding. Breed anything you have or get with leakage.
Make sense?