A Turkish Van may have blue eyes, amber eyes, or be odd-eyed (having one eye of each colour, a condition known as heterochromia iridis). The variability of eye colour is genetically caused by the white spotting factor, which is a characteristic of this breed. The white spotting factor is the variable expression of the piebald gene that varies from the minimal degree (1), as in the blue-eyed cats with white tip on the tail to the maximal degree (8–9) that results in a Van-patterned cat, as in Van cats, when coloured marks occupy at most 20% of the white background, but the white background in the breed covers about 80% of the body. Breeding two cats together with the same level of white spotting will produce cats with a similar degree of spotting.