I’m not sure about vulture hocks, but feathered feet and beards are both dominant traits. Her coloration could result from multiple crossings, not just birchen x something else.
I’ve never heard of black becoming less black. Though I have heard that serious breeders of splashes won’t breed them to other splashes, because it might make them paler/have less spots in the next generation.
If you are only using solidly colored blacks, blues, and splashes, you won’t get leakage. However, if the parents were color crosses or poorly bred, they could have chicks with leakage.
Splash is an off-white color with blue spots (never any other color of spots). When using splash in breeding...