You would prefer mauve, perhaps? Obviously dogs’ lips have to be some color, and black makes more sense than most.
According to veterinarian, Dr. Peter Ihrke, pigmentation helps protect animals against solar radiation damage. Because dogs don’t have as much hair around their mouths as on most parts of their bodies, pigmentation plays a particularly important role in shielding dogs against the ravages of the sun.
According to Dr. Kathleen J Kovacs, of the American Veterinary Medical Association, the gene for black pigment is dominant over the genes for all other pigments, so the presence of the black lips is attributable to hereditary factors. If two purebred dogs with black lips breed, one can predict with confidence that their puppies will have black lips too.
Not all dogs have black lips, though. Some breeds have non-pigmented lips and oral cavities.
James D. Conroy, a veterinary pathologist affiliated with Mississippi State University, told Imponderables that some dogs have piebald pattern of non-pigmented areas alternating with pigmented areas. The only breed with an unusual lips color is the chow chow, which has a blue color. Conroy says that “the blue appearance of the lips and oral cavity is related to the depth of the pigment cells within the oral tissue.”
From: When Do Fish Sleep? by David Feldman
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