Typically white areas on dogs will turn a brownish color due to an exposed area that gets wet on a regular basis. You will notice this on their feet and face, areas where they are exposed to moisture. You can use a peroxide/baking soda mix when you bathe your dog. Also, if you have a flat nosed dog, such a Shih Tzu, they need to really get into their food and water, and will need to have their face wiped after eating or drinking.
My terrie mix 1 year old dog is loosing hair and getting black spots of patches on his hair, why?