@Ariel
As per my experience with my patients,I am describing your the following

The color or your teeth may have nothing to do with cavities. Teeth are porous, like a sponge. You can discolor your teeth from food or beverages like beets, blueberries, mustard, soya sauce, red wine etc. If the pigment from these foods goes deep inside the enamel and into the dentin, you will have to whiten your teeth probably using some sort of peroxide. However, you can still get cavities even with white teeth. It is a function of bacteria in plaque giving off acids that dissolve enamel. Now, if you have not cleaned your teeth for weeks and the plaque buildup makes your teeth appear yellow, that is another matter.