RightBecause the genes are on the same locus, 2 parts of a whole so to speak - and a parent can only give 1 gene to the offspring from each locus. Each animal has 2 genes, 1 from each parent
So in the case of a Platinum it only passes one or the other, it can't pass both at the same time to the same baby. Same with a BEL, a Super Pastel, etc... any homozygous "super" form can't reproduce itself when bred to a normal.