Depending on age, a dog's coat can change colour. It's just like in humans - my son was born with almost white hair, it was so blond. When he was just under 2 years old it turned brown. He's 30 something now and his hair is still brown (although there's a little less of it now!)
It may also be a sign of a skin infection - is there any smell to the brown fur?
As your dog is older, it may simply be down to age.
I'd take her to the vets just to be on the safe side.
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Brown Tummies by: Kassie
That happened to my dog too. She was a golden cocker spaniel when she was born - not pure golden as she had a bit of brown on her back and her chest. Then she suddenly turned brown on her tummy - she's still the same, she never returned to her golden colour.
I don't really care as she's my dog and I love her the way she is.
