Though rabbits may seem like uncomplicated animals, they are more than simple sociable and inquisitive pets. The American Rabbit Breeders Association recognises more than 40 breeds, each with its own variations in colour, fur and ears. To produce the desired traits of a specific breed, a breeder has to be familiar with rabbit genetics, including those affecting eye colour.
How Eye Colour is Created
Rabbit eye colour is the product of the pigment melanin, just like fur colouration. In rabbits, the specific melanin pigments used are eumelanin and pheomelanin. The first is black-brown and the second red-brown. These types of melanin are stored within the cells of the eye and colour is created based on the amount stored and how widely it is spread through the cellular structure. Blue eyes in rabbits contain less melanin over a smaller area and because they spread out the reflected light, they appear blue despite the brown pigment. Brown-eyed rabbits have more melanin stored over a larger area, which condenses the reflected light more. However, it's the genetics of the particular rabbit which determines how much melanin is produced and stored.
Genetics determines a given rabbit's colouring, and often eye colour is linked to other genes which determine fur colouring. This is why different breeds of rabbit are given to blue or red eyes. Dominant genes are those which are always expressed, although sometimes other genes may modify them to some extent. Recessive genes are not expressed by themselves, but they may modify a dominant gene. The eye colours created by dominant genes are more common and those which are created by recessive genes are less so.
Among rabbits, the gene that produces brown eyes is dominant, and so the most common rabbit eye colour is brown. Brown eyes are preferred among many different breeds and are often considered acceptable for show rabbits, even if they're not the preferred colour. Varying shades of blue and grey are less common, but there are certain breeds --- such as the Netherland dwarf --- for which these are the preferred colour. Red or pink eyes are a genetic mutation, but through selective breeding they've become more common is some breeds than others. Still, red and pink eyes remain the least common.
Ruby-eyed whites, or REWs, are albino rabbits, and their red eyes are a product of their lack of melanin pigments. Because no melanin is produced, there is no colour and what we see is the colour of the blood vessels within the eye. This also makes REWs shortsighted, and because of this they sometimes "scan," weaving their heads from one side to the other as they try to bring an object into focus.