first cross Self Blue x Black or Black X Self Blue produces f1 Self Blues split to Black. All chicks are Black. They are, as you noted 50% Self Blue, but you won't get any Self Blues in the f1 generation. Breeding the f1's together will yield 25% Self Blue, 25% Black, and 50% Self Blue split to Black (Black chicks/adults). Since there is no way to tell the pure blacks from split, I consider the 75% Black chicks as culls assuming the goal to be improving the type on the Self Blues. You can breed a Self-Blue to a split and get 50% Self-Blues to up your numbers but if you are using a previous generation Self-Blue you aren't really improving the type with that cross. Anytime you breed to pure blacks, no matter if it's a split x Black or a Self Blue x Black you'll get all Black offspring.
