You don't say what color you're looking for, but if I read the rest of your post correctly your goal is Blue Mottled? If so, mottled is recessive and requires two copies to express. Of course Blue is incompletely dominant with one copy making blue, two copies making splash, and zero copies making black. With that in mind your program looks like the following.
Breeding Blue to Mottled is going to give you 50% Black and 50% Blue chicks. All the chicks will carry one copy of mottled. The quickest route to the most Blue Mottled would be taking Blues from your F1 generation and breeding them back to the mottled parent(s) as that would result in offspring that 50% would be mottled and the other 50% would at least have one copy of the mottled gene. And of course 50% of those would be Blue. If you took your f1's and bred them together, you would get 25% Mottled, 50% that carried one copy of mottled, and 25% that had no copies of the mottled gene. Note that there would be no visual distinction between those carrying mottled vs not.
