Why leaves change color in autumn?
Leaves are green because of the Chlorophyll, a pigment which is responsible for photosynthesis. There are other pigments also present in leaves such as carotenoids, anthocyanins etc. In summer, which is a growth season the chlorophylls is abundant in leaves and the green color of the Chorolophyll dominates the laef color. The colors of other pigments are masked out by chlorophyll. The chlorophyll are consumed and supplied during the growth season at equal rate and replenishment of Chlorophylls keeps the leaves green. This masking effect keeps the leaves green. During the arrival of the autumn, the leaf veins that carry fluids gradually get blocked, and the replenishment of chlorophylls gradually ceases. At this time, Chlorophylls get replaced at a slower rate than they are being used up. Due to this the hidden pigments of other colors are revealed. The orange-yellow colors are due to carotenoids, which are always present in leaves but appear only when chlorophyll disappears. Red, purple and other blended combinations are because of Anthocyanins.