color, is the most important pigment.
Carotenoids are pigments that create bright yellows and oranges in familiar fruits and vegetables. Normally, the chlorophyll covers the other two pigments- that's why in summer, leaves are green. However, as days get shorter, there is less sunlight, and as a result, less chlorophyll is produced in the leaves.
Finally, the tree stops producing chlorophyll completely. When that happens, the carotenoid already in the leaves can finally show through. The leaves become a bright rainbow of glowing yellows, sparkling oranges that give a forest a jewel-like appearance in autumn.
In autumn, the cool night temperatures prevent the sugar sap from flowing through the leaf veins, and down into the branches and trunk. Anthocyanins are produced as a form of protection. They allow the plant to recover nutrients in the leaves before they fall off. Anthocyanins give leaves their bright, brilliant shades of red.