The gums of a healthy dog are salmon pink, similar to skin colour. Some dogs are born with black spots on their salmon-pink gums, which is just a variation of that particular dog's gum colour. Any deviation from this normal colour is a sure sign that the dog needs to see a vet immediately. Get into the habit of opening your dog's mouth or watching the gum colour as the dog pants.
Discolouration of canine gums is often due to the blood flow getting blocked. It's the blood that makes the healthy pink or black colours. Infection, injury to the mouth, objects stuck in the mouth, sudden blood loss, poisoning, traumatic injury or inner organ failure can stop or reduce the dog's circulation system, which in turn reduces or stops blood from going to the gums.
Red and swollen gums indicate a gum bacterial infection such as gingivitis. If the gums are cherry red but not swollen, the dog could be fighting a poison. Pale grey, pale purple or white gums indicate shock, which requires immediate vet care. Yellowish gums can be a sign of liver problems. Blue or purple-blue gums mean the dog's body needs more oxygen immediately. White spots can indicate oral thrush and white lumps could indicate tumours.
Dogs with mostly black gums may only become discoloured in extreme emergencies. In order to check their health, gently pull down the dog's lower eyelid. The colour of the revealed tissue is a salmon pink that matches dog gum colour, no matter what the breed of dog. The colour underneath the lower eyelid is always pink in healthy dogs.
Dog gum discolouration usually happens along with other symptoms. For example, in heat stroke, the dog will collapse, the skin will be burning hot to the touch and the dog may stop breathing. Make a note of any other strange signs like diarrhoea, lethargy, vomiting, unusually bad breath, itchiness or swelling and point these out to your vet.
Although accidents can be hard to prevent, many causes of dog gum discolouration can be prevented. Feed your dog hard, crunchy foods to help clean plaque off of the dog's teeth. Teeth should be brushed three times a week using a toothpaste made for dogs (human toothpaste will make a dog vomit). Keep all medications, household cleaners, insecticides, paint, car fluids and other hazardous materials out of a dog's reach. Do not leave a dog in a parked car when it is hot outside. Keep a dog fenced so that he cannot wander out into traffic.