Why do leaves change color in Autumn?

Autumn leaf color is a phenomenon that affects the normally green leaves of many deciduous trees and shrubs by which they take on, during a few weeks in the autumn season, various shades of yellow, orange, red, purple, and brown. Sugar maple trees are deciduous and use their broad green leaves to absorb sunlight which is converted to sugar. Chlorophyll is a green pigment found in leaf cells giving them their green color. In the summer, chlorophyll absorbs energy from the sun and the roots absorb water and minerals from the soil. 

In the process of photosynthesis, a simple sugar is produced, which is converted to starch, and is stored within the tree. Pigments can absorb light from the sun and use it for photosynthesis. Sugar Maple trees also contain other pigments called carotenoid, which are yellow/orange pigments, and anthocyanins, which are red pigments. The last two pigments are not seen in maple trees all times of the year, mostly because chlorophyll is highly expressed the rest of the time essentially washing out the other pigments. As the days get shorter, and the nights get longer in Autumn, there is less sunlight to absorb. Then the bright green pigment lessens and allows the yellow, orange and red colors to come out.