Let's face it: the majority of dogs have brown eyes. In dogs, there's really not so much variety when it comes to eye color compared to humans, other than various shades of brown and some very few breeds who boast blue eyes. Even among other types of animals, other than cats and some types of birds, it seems like brown eyes are the most common color.
With dogs coming in so many different colors, shapes and sizes, it may seem a tad bit odd that things are so limited in the eye color department.
A Matter of Melanin
Eye color is determined by the pigmentation of the iris, the circular structure surrounding the pupil. Iris pigmentation tends to vary based on the concentration of melanin in the front layers of the iris, so the more the melanin concentration, the darker the eyes will be.
This means that dogs with brown eyes have a larger concentration of melanin in their iris, while dogs with blue eyes have much less. Melanin is what gives color to a dog's skin, coat and eyes. It protects the cells by trapping light rays, preventing them from harmful radiation.
Without melanin, dogs would be albino, which means they would have a white coat, pale, pink skin, and possibly, pinkish eyes.
Age of Onset
Because melanin production doesn't start at birth, most puppies are born with blue eyes. The blue color is gradually lost as the permanent eye color shows up by the time the puppies are about 2 months old, explains Stanley Coren in his famous book: "Do Dogs Dream? Nearly Everything Your Dog Wants You to Know. "
By this timeframe, most puppies will have brown eyes. When the eye color doesn't change within this timeframe, there are good chances the blue eyes will be there to stay.
For example, according to Powerscourt Cocker Spaniel Breeders, in the case of a puppy with a merle coat, the blue eyes are not likely to darken because the merle gene dilutes the pigment, therefore the blue eye color will be permanent in this case.
Coat Color Effect
Interestingly, some shades of brown are only seen in dogs with a certain color of coat. According to Dog Genetics, all liver dogs have amber eyes. Liver dilutes a dog's brown eyes to amber.
In addition to amber eyes, the liver gene typically causes dogs to have a light brown nose. The amber eye color may range from a light brown to yellow or almost grey as seen in the Weimaraner, a liver-pigmented dog breed also blessed with the dilution gene, giving it the typical "gray ghost" appearance.
Amber eyes are also seen in breeds bearing a blue coat color and occasionally amber/copper eyes are also seen in dogs with black pigment.
A Softer Look
Dark brown eyes are very common in our companions and if we take a look at most breed standards we will notice that most will call for dark brown eyes. Yet, curiously, if we look at the eyes of canines in the wild, we will notice that most of them have lighter colored eyes compared to the average domesticated dog.
For instance, the wolf, the dog's ancestor, was provided with an eye color that is generally gold, sometimes amber or light brown and with hues of yellow or even grey, notes Lisa Dube Forman, an American Kennel Club Dog Show Judge for Irish Wolfhounds and Afghan Hounds.
Dogs therefore were likely selectively bred to have darker eyes because of cosmetic appeal, as the yellow ‘bird of prey’ color gave dogs a hard, unappealing look.
Did you know? The "bird of prey" eye color is considered a fault in many breeds. For instance, this eye color is considered a serious fault in the Rottweiler breed and may even lead to disqualification in the cane corso and Polish lowland sheepdog breed.