Anything's possible, but I'd be surprised if it was. It's not uncommon for dogs to have dark pigment in their mouths--roof of mouth, gums, and even tongue. Chows have all black mouths and tongues, and other breeds and mixes have dark pigment to a greater or lesser degree. (The shitzu mix sitting beside me as I write this is more dark than pink.) If it concerns you by all means have it checked by your veterinarian. If not, checking a dog's mouth is or should be part of an at-home monthly check-up done by all dog-owners (you can read more about this in my book, DogSmart). Doing this will enable you to keep track of these areas in case any change does occur in them.
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