So I had a litter of mice a few weeks ago that had a black, gray, and 2 brown mice in it. I was pretty happy because all my mice are white and I had not seen any genetic differences before, over time I ended up feeding off all but one black male.
He was the "alpha" of the litter, and was super sketchy. He would BOLT and hide whenever anyone came up to the cage, and would run from you if you tried to pick him up (He never bit/lashed out, just tried to run off) and he would "bully" some of the other mice (Never anything huge, just mild fighting that never amounted to anything, and he would hold down the other mice and clean them often).
I kept him in my small colony longer than the rest because he was very healthy and a seemed to be a good breeder minus his quirks.

Fastfoward a month or so to now, he has been fed off along with all my other mice, other than 3 pregnant females I had. Now one had a litter 1-2 weeks ago, and the others just had tiers the other day. The one who had them a few weeks ago, they finally started to have fur come in..and I'm happy with the results!