Was this part of my tooth or a filling?

I lost a small piece from the top outside part of one of my back teeth, close to my gumline. It looked white on the inside and black on the outside. I've tried to look at my tooth, but I can't really tell if it's black or not, certainly doesn't look like it. A small section of my gums are just a little tender, but otherwise it feels fine.
Is there a reason if it was a filling it would've been black?
Or if it was my tooth, shouldn't I be in pain?