Since I think blue is the harder colour to get and stabilise in shrimp it should be relatively easy to breed yours back to black. You may have to take lots of macro shots (and if possible have the camera setting on true colour or something like that, mine has it to capture the true hues of sunset), and be ready to remove any that don't meet your standards/ requirements.
The reason I warn about the colour setting on the camera is that depending on tank lights, ambient light and angle of the camera you can get very drastic colour variation on the same creature. Since I have a slight colour blindness I find it easier to A try grading shrimp in real sunlight and B bug my Husband into coming and checking and confirming my colour suspicions. A hand held magnifying glass can also be useful.
If the shrimp you where given where not throwing 100% black offspring then I would suspect that you will end up getting a lot of chocolates with or without some black on them, Blacks with patches of dark blue and even the odd semi-clear wild type.