Beneath their coats, dogs have a variety of skin colors. Changes in this color means that something is changing within the dog's body.
A yeast infection will cause the skin to get darker in some places. Vets call this condition hyper pigmentation. Changes in color are also caused by friction. When pets lick of scratch the same area over a long period of time, because of allergies for example, pigment producing cells in the area get overactive, and the skin looks darker.
A number of the body's hormones, including those produced by the thyroid and pituitary glands, play a large role in regulating melanin, the skin's natural pigment. Pets with hormonal imbalance may produce too much melanin, causing the skin to get darker in some places.
But ,,,Go to your vet and get it checked out!
My dog just became pregnant, and her whole stomach gradually turned dark, then black. Even her nipples went from soft pink to black.
Over heard the sales person in the pet store telling someone it had to do with the food they were feeding their dog. I didn't pay much attention but they seemed quiet knowledgeable about it as though it was common and a sign of improper food.
Take him to the vet. They might have a solution.
My dogs stomach turned from pink to black and I think he has a tick cause he keep moving her head like it tries to shake something of of it.
Allow a vet to check your animal to give you a reason for this happening....the best to you
It has probably eaten something wrong