I don't know how old Bramble is, but if she is old enough she will turn gray. Nor sure if that is the case here.

Our RB Flicka started to turn gray at about 15 a little, and it accelerate as she got older. She never got gray like Bramble, hers was more of individual gray hairs like humans get. What was strange with Flick was that when she hit about 19 or so she started to get a red hue to her fur. It was the stangest thing. The red continue to deepen until she passed on at about 21. Up until that point she was pitch black.

Ok, too much information I am sure.