Why do leaves change color in autumn?

The answer

Leaves are green because chlorophyll, the pigment used in photosynthesis, dominates and masks other pigments. As days shorten in autumn, trees stop producing chlorophyll and it breaks down, revealing yellow and orange carotenoid pigments that were present all along. Red and purple colors come from anthocyanins, which are newly produced in autumn in response to bright light and sugars trapped in the leaf. The specific mix of pigments creates each species' unique fall palette.