To have a chance for a red calf from black cows or grey smoke cows, the cow has to be a red gene carrier (could be black with a red gene as black is dominant or could be a grey smoke if it is a red carrier or could be a red, which has two red genes or it could be a red or yellow smoke, which has two red genes). If you use a red bull and your cow is red, you will get a red calf. If you use a red bull and your cow is heterozygous black, then you have a 50/50 chance of a red calf. If you use a red bull and your cow is homozygous black, then the calf will be heterozygous black. The smokes are from the diluter gene and that adds another twist that, as far as I know only dilutes the base color.