There are around half a dozen genes that combine to give your rabbit its colour. Some Breeds, like the Holland Lop and the Netherland Dwarf depend on the dwarfing gene to give the rabbit the size and proportions to meet the show standard.
Genes are in pairs and when one of the pair is defective, the other often makes up for it.
Rabbits, particularly ones from related parents can carry pairs of defective genes which can be problematic or fatal. Sometimes truth is stranger than fiction.