You say that your cat has already lost some teeth. Your cat is 13 years old. Dental disease, gum disease and oral health problems are somewhere near the top of the list of health problems and pets. You only have to go to a veterinarian’s photo stream to see many pictures of cats and dogs with gum disease. Teeth should obviously be white as an enamel is white. Either your cat has gum disease that requires the attention of a veterinarian or it is possible that there is black pigmentation in the gums or in the area around the gums. However, bearing in mind your cat’s age this would appear to be gum disease. Gum disease can make the mouth sore for a cat. Please remember though that your cat will be placed under general anaesthetic if teeth are cleaned and removed. Placing a cat under anaesthetic does have risks. You are probably aware of this.