Grey tooth?

Ka

I go to the dentist every 6 months and I have an appointment next month. For the last week or so when I eat harder foods and bite down with my back tooth it shoots this pain through my tooth really quick so I decided to look and it looks like it’s turning grey. Should I try and get an earlier appointment and call Monday or just wait until next month for my appointment? I brush my teeth twice a day and I’ve never had problems since I was a kid.