I saw a man with this same condition today. Can you guess what it is?
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It's vitiligo! It is a condition that causes progressive depigmentation of the body and can affect all areas that are pigmented, including hair/fur, skin, and eyes. The rottweiler above has lost pigment from its nose and around its eyes. Vitiligo is occasionally seen in dogs, and is known to occur relatively frequently is breeds such as the Doberman pinscher. In humans, it is more easily noticeable in individuals with darker skin pigment as in the image below. It is believed Michael Jackson may have had this disease.
Images are from Wikimedia Commons under a creative commons license: one, two