It's a bit arbitrary. Enough people don't want tomato and so you get a "pizza bianca" without tomatoes. Enough people don't tolerate mozzarella so you've got "

It's a bit arbitrary. Enough people don't want tomato and so you get a "pizza bianca" without tomatoes. Enough people don't tolerate mozzarella so you've got "pizza rossa" without mozzarella. I guess that a pizza without both mozzarella and without tomatoes may be considered by most to be just a focaccia but I'm pretty sure somebody will point out some place in Italy where that's how they make the "true pizza" anyway