@tanza
First, I responded to the first post and missed the rest of this. So ignore rescue suggestion.
And absolutely responsible breeders decide who gets what puppy!
Yes, there have been some studies linking temperament in mammals to colors. But the issue was more related to the " popular stud" syndrome than a genetic tie between color and temperament.
Second thought is Shirley disagreeing about being handled in the show ring equaling good temperament. Having personally met a few Lhasa Apsos and talked to a few Westminster competitor breeders, there are some utterly nasty ones who like the ring and tolerate handling. Also, there was a Rottweiler champion who was so human aggressive out of the ring he was legendary.
But obviously breeders want a solid temperament. In today's world with the internet, bad temperaments will sink your reputation.
On culling, in farm animals it often meant kill. In Germany, the club dog wardens used to require large litters to be culled. They stopped a long time ago, but GSD and Rottie people still talk about it. But in dog breeding, it's generally remove from the breeding pool. Though a lot of Bulldog breeders euthanize pups with cleft palates. I guess I do not want to pretend culling never means killing.