Yellow Jacket looks like he's working very well. I think breeding him to clean fronted cows is the key. I've never used him, but I've seen enough that I'm pretty impressed.
Yellow color "more or less" means that he's a "red smokey". In other words, he has 2 red genes instead of a black gene or he would be a smokey. The gene that causes white in Charolais turns red to yellow, orange or white & it turns black to light smoke/ or smokey grey. It's similar to the diluter gene in Simmi's, but it's not the same gene. The way you tell if the animal is black is if it has a dark nose. If it's red it will have a pinkish nose. Charolais are white in appearance, but they are really red gene animals.
Anyway, bred him to homo blacks & you should get black & smokes. Bred him to hetro blacks & you could get black, red, smoke, yellowish or possibly even white. Breed him to red cows & you will get red, yellow, orange or white. I've heard that bred to Shorthorns that you can end up with "peach", because they have a different gene that effects color too.