The D Locus has two different alleles in it: ‘D’ and ‘d’. ‘D’ is the most dominant, and ‘d’ is the most recessive.
D: Dense
d: Dilute

Gene involved: MLPH (melanophilin) gene (Fontanesi, 2021)

DENSE
The ‘D’ allele is the Dense allele. All non-dilute rabbits must have at least one of these alleles. If they have two of these alleles, then they are homozygous (Meaning it is “pure” for that allele, so that it cannot produce anything recessive to it no mater what it is bred to.) for Dense. The following are examples of varieties that have the Dense allele:

Chestnut, Castor, Sandy Gray, Copper, Gray, Chocolate Agouti, Cinnamon, Red, Orange, Black/Orange Tricolor, Chocolate/Orange Tricolor, Black Japanese Harlequin, Chocolate Japanese Harlequin, Black Magpie Harlequin, Chocolate Magpie Harlequin, Tan (Black, Chocolate), Otter (Black, Chocolate), Black, Chocolate, Tortoise (Black, Chocolate), Marten (Black, Chocolate, Sable), Seal, Sable, Siamese Sable, Sable Point, Siamese, Black Himalayan, Chocolate Himalayan.

Dense can carry dilute.

DILUTE
The ‘d’ gene is the Dilute allele. All dilute rabbits must have two of these alleles. The following are examples of varieties that have the Dilute allele:

Opal, Lynx, Fawn, Cream, Blue/Fawn Tricolor, Lilac/Fawn Tricolor, Blue Japanese Harlequin, Lilac Japanese Harlequin, Blue Magpie Harlequin, Lilac Magpie Harlequin, Tan (Blue, Lilac), Otter (Blue, Lilac), Blue, Lilac, Tortoise (Blue, Lilac), Marten (Blue, Lilac, Smoke Pearl), Blue Seal, Smoke Pearl, Blue Point, Blue Himalayan, Lilac Himalayan.

Dilute cannot carry anything. It must be pure for dilute in order to be a dilute variety.

References PDFs