The Basic Shades
Understanding rabbit coat color genetics is easier if you look at it in chunks.
We'll start with what I call the “basic shades”. These basic shades are controlled by two sets of genes: the Chocolate Gene, and the Dilution Gene.
Chocolate - B gene
This gene has a lightening effect on eumelanin only. I.e, it has no effect on red-based colors. Like most furred animals, rabbits have two alleles for this gene, with symbols B and b respectively. When B is present (BB or Bb) the brown/black eumelanin is its normal, unlightened, color: Black. But when a rabbit is bb the brown is lightened to Chocolate.
Dilution - D gene
In its recessive form, this gene has a diluting effect on both eumelanin and pheomelanin. When present in the homozygous recessive form (dd) it dilutes brown eumelanin to blue, chocolate to lilac, and red to cream.
The four basic shades are:
Black (B- D-)
| Castor (Black Agouti) | Black Otter | Self Black |
|---|---|---|
 |  |  |
Chocolate (bb D-)
| Amber (Chocolate Agouti) | Chocolate Otter | Self Chocolate |
|---|---|---|
 |  |  |
Blue (B- dd)
| Opal (Blue Agouti) | Blue Otter | Self Blue |
|---|---|---|
 |  |  |
Lilac (bb dd)
| Lynx (Lilac Agouti) | Lilac Otter | Self Lilac |
|---|---|---|
 |  |  |