Crap...hit the wrong button. What I have found before is:
Black x Black = 100% Black
Splash x Splash = 100% Splash
Blue x Blue = 25% Black 50% Blue 25% Splash
Blue x Black = 50% Blue 50% Black
Blue x Splash = 50% Blue 50% Splash
Black x Splash = 100% Blue
Again this is a black cochin hen to...