Blue eyes are normally associated with white coats. Blue-eyed-white-coated cats are rare — less than two percent of all cats. The coat and eyes result from a specific genetic factor causing low melanin production. The same stem cells create both coat and eye color and are affected by the same low level of melanin. The effect on the eyes involves both the pigmentation of the iris and the way the light refracts through the eye. As a result the intensity of blueness varies between cats.
In Siamese the blue is also associated with the light coat, and melanin production again is involved. However, in this case the gene is different and causes a kind of partial albinism. In this case the temperature of the cat determines the melanin level and therefore the color.
Domestic cats may sometimes show this pattern. Three cat breeds that often have this color combination are the Turkish Van, Turkish Angora and Khao Manee. The Turkish Van and Turkish are natural breeds and the Khao Manee an ancient Thai breed. In each case the most prized cats are those which are have one blue eye and another odd. The odd eye may be green, yellow, amber or gold. Many cultures believe such odd-eyed cats bring good luck.
White cat breeds with blue eyes: a rather lovely Angora showing its one blue eye
Are there blued-eyed-cats without white coats? This occurs but is unusual. A relatively new breed, called the Ojos Azules has this pattern, though other individuals have been recorded. The Ojos Azules breed comes from Mexico and a small colony of cats of the type were found living wild in 1984. An attempt has been made to establish this as a new breed.
According to Wikipedia:
Ojos Azules are remarkable for their deep blue eyes. Unlike the blue eyes seen linked to the genes in bicolor cats and cats with point, both of which suppress pigmentation, this gene is not linked to any certain fur color or pattern, giving the opportunity to have cats with dark coats and blue eye.
It is very possible that the deep blue eyes of this breed could become more common in the future. Even if this happens, white-cats-with blue eyes will almost certainly remain very special.