Tooth colour is affected by the way that the teeth scatter, reflect and absorb light. As ardent drinkers of coffee and red wine will know, the outer enamel layer of teeth can easily stain, giving teeth a yellow hue. However, what’s inside counts too. Since enamel is fairly translucent, the underlying yellow dentin plays a major role in tooth colour. Baby teeth appear white because the dentin is paler in colour, so it doesn’t show through the enamel as much. However, our luck runs out with adult teeth. The dentin is darker and enamel tends to thin as we age, letting dentin’s colour shine through. Some medications, such as tetracycline antibiotics, are also known to cause teeth to turn yellow.