Dog skin pigmentation changes

My two year old Rhodesian Ridgeback (male, castrated), who has always been healthy and never suffered from any skin problems seems to have developed dark patches of skin under the white fur on his chest.  Seems to only be under the while bits of his coat.  The patches are not angry irritated or raised, just darker, black or brown.  The colour of the hair has not changed and remains white.  Is this a common occurance? - From what i have read it would not seem sinister as ths skin is not ulcerated, but would be interested in any similar experiences you may have had. thanks.

[Katra23]

You should take him to the vet. This past Saturday I took my dog to the vet we have been trying to treat him for a infection from a dog bite for a few weeks. It has been hard to treat the infection so the doctor started to look for another condition that may be causing his infection not to heal. The vet asked us and looked for dark ( black or brown) spots on my dogs skins because it can be some sort of disorder. I am not sure what it could be but  he asked if we have noticed and black or dark brown spots on his skin.

[Misfits4Me]

The disorder is that of either "Hypothyroidism" or "Hyperthyroidism". In other words: Have his Thyroid checked...It can lead to many things other than discoloration of the skin. Look it up, you may find other symptoms that fit, also.....(Including infections that won't heal!)  Good luck to you both.......Karla