My Yellow Lab Has Horrible Bad Breath And Her Mouth Is Black On The Inside.Her Gums Are Pink,so Is Her Tongue,the Rest Is Black. What Could Be Causing This?

Likely what you are seeing is severe dental tarter.  Dental tarter is bacteria that mineralizes to the tooth.  It causes gum line recession, bone loss over the tooth root, and abscessed teeth.  Typically tarter is more brown in color but can be very dark.  This is likely what you are seeing if the problem is generalized ie throughout the entire mouth.  If the black color is located to one specific area I would be concerned about an oral melanoma or other type of tumor.  Either of these conditions can cause very bad breath.  
Your dog needs to be examined by a veterinarian and have a dental cleaning done.  It is likely your dog will require extractions if the disease is as severe as it sounds.  This procedure requires general anesthesia.  Further information will be given to you by your veterinarian.