The pigmentation in the skin indicates a chronic condition which could be caused by a variety of things such as chronic allergies (food, inhalants, or fleas). It could also be the result of hormonal imbalance such as low thyroid. I would suggest you give Derma-IonX, a probiotic, and a grain-free diet or a commercially prepared raw food diet. These will positively impact most of the above conditions.
In addition, I would use a flea comb on the coat to look for evidence of fleas or flea debris. Sometimes allergies are aggravated by fleas. Our Defendex shampoo helps rid the pet of fleas on the body and helps to cool hot irritated skin, providing relief. If you see any evidence of fleas also treat the dog's environment with a flea product containing an insect growth regulator.
Hope these suggestions are helpful. Please keep us informed of your progress.