In autumn, nights become longer and days shorter. The leaves are exposed to very little sunlight and the green colored chlorophyll production is reduced. So, the colors of the existing carotenoids (yellow,orange, and brown pigments) in the leaves show up. During autumn, the excess glucose trapped in the leaves combine with sunshine to produce the red colored anthocyanins. These chemicals show up as myriad colors in the leaves such as Maple and more.