A great way to do it that still allows you to relax is to have two tanks per colony. Tank A, and a tank B (or more later on)
Tank A will hold your best colored shrimp of that strain, Tank B will be your less colored.
Tank A will be your concern for selective breeding. Keep only the best of your trait in there and cull the rest of the babies into Tank B that doesn't match your standard.
You will work on your bell curve with Tank A.
Here's the trick- DON'T move from Tank B into A again. You can start another tank (A2) if you'd like to work parallel to A.
Why?
You are slowly gathering the modifiers together into alignment of the trait you want in Tank A. If you move a different tank shrimp into Tank A, it has stuff genetically in the background that you don't want. (The relatives were not bred for your goal.) It sets you back and costs you time. If you keep adding from Tank B, you may never reach your goal.
Now the advantage of a Tank A and a Tank A2 (if you decide later), is that if- in time- they are displaying similar desired traits, you can switch out shrimp between the two and you can increase diversity, but it is not a necessity.
Clear as mud? LOL