First of all, you need to know that enamel is the outer layer of your teeth and is generally white to whitish-blue-gray according to dentist Harold Katz, DDS, founder of The California Breath Clinics. The layer just beneath the enamel is called dentin and it becomes visible as the outer layer (the enamel) becomes thinner. It’s color? – YELLOW. Check out what habits are yellowing your teeth!