Although your dog might like to believe a changing of skin color means he's turning into a super dog, the true reason for his darkening pigmentation isn't very exciting. From skin conditions to skin infections, dark skin is a medical condition that you and your vet can probably easily manage.
Dogs, as different as they are from people, suffer from similar allergies, like grains and pollen. The allergic reaction that plagues your pup makes him scratch, and his skin usually appears reddened and sometimes scabs appear. If left untreated, those pesky allergic reactions can eventually progress and, along with all that licking and biting your dog is doing, cause his skin to break out into blotches of black and purple spots, also known as hyperpigmentation. Treating the allergy stops those nasty spots in their tracks. Your vet might test your dog for allergies and give him hypoallergenic food.
Hypothyroidism might sound bad -- and if left untreated it certainly can cause harm to your dog -- but it's easily managed with medicine. It happens when your pup's thyroid gland produces less thyroxine, which is a hormone, than normal. That's bad news for your little guy's skin and coat. His skin may darken in certain areas, and if the condition progresses, the darkened color can appear all over his body. He'll also turn from your furry friend to a somewhat furry friend, losing patches of hair, and he will also likely scratch himself more than normal. A trip to your vet can confirm hypothyroidism.
Let's face it -- paws and nails can only do so much. Everything else needs to be investigated by your pup's tongue. But while one lick will usually do, some dogs take things a little too far and incessantly lick their paws, stomach or other areas of their body. The constant licking irritates your pup's fur and skin, causing his hair to fall out and his skin to redden and darken. The affected area can become very painful for your pup. While licking is often an indication of an allergic reaction or other skin condition, your dog may just lick when he's nervous or for seemingly no reason at all. Always see the vet even if you think your dog's darkening skin is due to licking, to be sure he isn't suffering from another problem and to get something that will discourage the licking.
While it would be great for everyone involved if every skin condition had unique symptoms, most borrow from one another and look similar, as is the case with a yeast infection. But while scratching, darkened and reddish skin can point to a yeast infection or a number of other problems, WebMD notes yeast infections often occur in your pup's paws or ears. If the condition worsens, you'll probably notice a nasty yellowish discharge coming from the affected area as well as crusty skin. If your vet diagnoses your pup with a yeast infection, he'll probably send you home with some anti-fungal medicine that will knock the nasty fungus out of commission.
While neither you probably don't want to hear there is a long list of conditions that cause hyperpigmentation, the good news is your vet will usually set your little guy on the fast track to recovery. Hormonal imbalances, skin infections, genetics and even parasites can lead to the unsightly darkened skin. A few tests can usually pinpoint the issue, and ointments or a few pills can control most problems.