Because Chows are the dogs most known as having black or black-spotted tongues, some mistakenly assume that a dog with a black tongue is a Chow or at least part Chow. In reality, there are many other breeds of dog that may have black spots on their tongue or gums.
The Chinese Shar-Pei (commonly referred to as the 'wrinkle dog') is another breed that is known to have a black tongue. Many breeds are known to have tongues or gums with black spots, prompting less knowledgeable owners to think they may have a dog that is of mixed parentage rather than a purebred.
The following breeds are ALL known to have black tongues:
Airedale (If purebred, they only have black spots, not an entirely black tongue and it does relate to Chow Chow bloodlines in the breed development in this situation)
Akita
Australian Cattle Dog
Australian Shepherd
Belgian Sheepdog
Belgian Malinois
Bichon Frise
Bull Mastiff
Cairn Terrier
Collie
Cocker Spaniel
Dalmation
Doberman Pinscher
English Setter
German Shepherd Dog
Golden Retriever
Gordon Setter
Great Pyranees
Irish Setter
Keeshond
Labrador Retriever
Mastiff
Newfoundland
Pomeranian
Pug
Rhodesian Ridgeback
Rottweiler
Siberian Husky
Tibetan Mastiff
as well as several other breeds that are less well known.
The black spots on a dog's tongue are a result of excessive pigment, much the same as freckles or birthmarks in people.