No one answered the real question here.....
If you have a parent that is any other color than black, you cannot increase your odds of having black calves.
The further you get away from the charolais parent, the better luck you will have with black hided calves but it is still a crap shoot. I do know that red is recessive and black is dominant, so it can be hiding alot of things underneath. WHITE coat color in the charolais is an inhibitor, it prevents color from forming. SO if you have a purebred charolais parent, then the calf will always express that in some degree.....being orange, yellow, gray, mouse, smoke colored or whatever.
I have many charolais mix cows, most originated from one charolais x angus cow, Trisha. She is a light tan color Several of her daughters are darker tan or smoke colored (when Trisha was bred to a black bull) and in turn their calves have been black or smoke colored also (when bred to a black bull) This year, I bred Trisha and her oldest daughter Sam to a gelbvieh bull. Trisha (the first generation charolais cross) produced a BLACK calf. Sam (the 2nd generation cross, who is 3/4 angus) produced a gray colored calf.
Point being, you need to get a few generations away from the purebred charolais to take out the color on a more consistent basis.
I agree with you that the charolais genetics really increase frame size and all the calves we keep to butcher are generally charolais. If I have to send them to an auction house (I prefer not to, but sometimes I can't sell them all privately) I have some really good looking grass calves in black packages that bring good prices.