Most of us Black Americans are incapable of producing a 100% black child because we're not 100% black to begin with. I suppose you could try to find the darkest woman possible to maximise the blackness of the child, but that would mean never mating with light to medium skinned black women, which is not very pro-black at all.
As a matter of simple math/science, having any children at all spreads black genes equally. You contribute about half the genes to a child regardless of the race of the partner. Therefore it's more a matter of quantity than percentages. If you wanted to spread black genes the most, you would knock up as many women as possible, regardless of their race. That is an exercise in futilty and totally irresponsible.
Pro-blackness through procreation is silliness.