In the UK when a rabbit population reaches excessive proportions we can also get black rabbits appearing occasionally, and no one can come up with a satisfactory answer , some say it is a "throw back to an older race". Or inbreeding causes " melanistics " . I lean towards this theory. What is strange is that these black rabbits can appear anywhere ,We have them miles from anywhere up in the hills on the ground we shoot, they can just appear. And the likely coincidence that each population had a black rabbit escapee mix with them is too much to believe. They can appear anywhere in the UK. My reason for not believing in the escapee theory is that white rabbits are more commonly kept as pets, yet we NEVER see white "wild" rabbits.