My 10 and a half year old Yellow lab mix's fur recently started turning a rusty red around her mouth and, umm, her her 'bottom' area. I just noticed it about two weeks ago, and it appears to be darkening. On her mouth, it is right next to her gums, and appears most around where her canines touch her fur. I am wondering if this is something I should be worried about. She hasn't had any recent diet change, and my other dog doesn't have it. They are eating TOTW High Prairie and Wetlands formula (we alternate). Their hasn't been any other changes that I can think of right off the top of my head. Any suggestions would be great!