you got it. Since you have only males with the trait, you cant make anymore. Your colored females are just being used to create offspring with the trait that the original males can breed with. Like they all said, those F1 might not show the Phenotype of that trait (cant see it) But they should have the genotype (Genes) to pass on. Then when the original males breed with the F1s, some proportion of THOSE offspring (F2) should show the Phenotype.
As an example, human eye color is really nice. Brown is dominantand Blue is recessive, just assume thats all the colors there are lol. Your white shrimp are like blue eyes(most likely) recessive and the normal color is dominant.
If mom has brown eyes B~B
And Dad has blue eyes b~b
When they have kids, they will be
b~B And since B is dominant, it covers up b and All the F1s have brown eyes. But they have the b gene now. If we broke a few laws then their kids could have;
(F2) would be
b~b which would look like 3/4 of the kids with brown eyes and 1/4 with blue.
Right now you have 2 dads with b~b, if one was a female it would save you a whole step. but your well on you way already.
I hope that all came out right, I will change it if I confused anyone...
Edit* You sure can just leave the white males with the F1s also, it will just make things move faster.