The D-Locus or sometimes called dilution, effects expression of other feline coat color genes. There are two D-locus alleles: dominant “D” and recessive “d”. The dominant “D” allele expresses full density, not effecting coat color. Cats with this dominant allele have darker or fuller color compared to cats with two recessive alleles. Two recessive “d” alleles are needed to express a diluted color. Recessive expression of black cats appears blue, as seen in Russian Blue Cats.