Hello, my dog has been tested for hyperthyroidism. Everything is clear. No signs of allergies either, no changes on her appetite, or weight. Energy level is the same. Overall nothing seems to be wrong. But is so strange her skin pigmentation is turning black. Everywhere else in her body her skin is pink. All the sudden the pigmentation spread. When I saw a small area around her neck about a month ago I thought it was her collar rubbing her skin. But a month later the grayish color spread through out her entire back. She hasn’t lose any her from her hind legs of genital area nor skin pigmentation. Is just her back. Note: my dos is a spayed Cocker Spaniel (9 years old). Thank you in advance.