Your "Black roo" is a Blue Cockerel. You can breed him to a Black. I won't comment on whether you should because I don't know what it is you want out of such a breeding. Chart that follows gives the likely results of such breeding.
Blue to Blue = 50% Blue, 25% Splash, 25% Black
Splash to Blue = 50% Blue, 50% Splash
Splash to Black = 100% Blue
Splash to Splash = 100% Splash
Blue to Black = 50% Blue, 50% Black
Black to Black = 100% Black
I showed a picture of a young pen I am going to sort through. I may only get 1 quality bird out of that pen when I am done or it could be 10. Only time will let me know which it is. That will take several more months. I have sorted out several already for non straight combs and feet that are not bright yellow on the bottom. None are old enough to have had eye color change yet. Sorting for eye color and wings will come later.