Himalayan rabbits have light coloured fur with dark extremities, such as the ears, nose, paws and tail.

The dark extremities are caused by the recessive Himalayan gene (ch). Himalayan rabbits are known to be homozygous recessive (chch) for this gene, which is involved in the production of melanin. Experimental evidence suggests that the enzyme produced by the Himalayan gene is active only at low body temperatures.

Therfore, the black fur only occurs at the extremities where the body heat is lower. [Extemities are colder because they lose more body heat to the environment.] Perhaps this is an ancestral trail where the dark extremities are less likely to freeze because they absorb light and solar heat.

The activation of the temperature-influenced Himalayan gene has been demonstrated by shaving off the fur on the back of a Himalayan rabbit and applying an ice pack. The new fur that grew in was black instead of white, showing that the enzyme controlling melanin production is active only at low temperatures.