I wouldn't worry. That is typical for their mouths to be black on top as far as I know. I have seen many dogs with black gums/roof of their mouths/under their tounges.
Bella had 8 double teeth taken out last Monday. I was so worried about it! She had already been spayed and they thought they would fall out, but no luck!
So she had to go under general anestisia again
! She did great though. When she came home she was sleepy and I did water down her kibble a bit, which she ate with no problem. By day 3 she was back to eating her food without water in it and the bad breath was gone IMMEDIATELY! Not to worry...your fur baby is just fine!
If surgery has to happen, it seems to be very routine and easy on the dog!
Hope this helps!