If the mouth(gums) or tounge turns white, most likely thing is the heart isn't pumping properly for what ever reason. You notice the lack of blood in those areas first cause the rest of the body is covered in hair. Have it checked out by a vet. My dog has episodes where his heart goes out of rythm and he drops to the floor, acts like he's dizzy(which he is from lack of oxygen). Gets back in rythm within 2 -3 minutes. Hasn't killed him yet but could. Vet says its brought on from over excitement. Once he calms down he's ok.
Lack of blood to the mouth and Tonge
If your dog has been poisoned or its heart skips a beat. White gums indicate that blood is not flowing normally. See a vet
My dogs tongue turned white and his eyes were very dialated what is wrong he wouldn't move?
An over abundance of parasites and anemia is one thing that can cause it