Dog breeds likely to have spotted tongues include Dalmatians, German shepherds, golden retrievers, collies and Labrador retrievers. Spots on a dog's tongue, usually ranging from black to blue in color, can occur in any breed, but some dogs are more prone.
The spots found on dogs tongues are the result of heavy pigmentation, or the coloration found in animal cells. This occurrence mirrors freckles or birthmarks commonly found on a person's skin. Pigmentation can affect other parts of the dog including its lips, nose, eye rims, pads and toe nails; this kind of pigmentation in dogs is genetically determined.
Some breeds, such as the chow and the Chinese shar-pei, are specifically bred to have a blue-black tongue and mouth as part of their pure bred standard. When other dogs breeds have a random pattern of black spots on their tongue, it is a case of pigmentation from other areas of their body, such as their lips, carrying over to their tongues.
Flat, black spots on and around a dog's tongue are perfectly normal and typically tend to grow and change shape over the years. Black spots that appear to be raised or bumpy should be checked out by a veterinarian.