Yellow and orange hues come from carotenoids, pigments that are present in leaves throughout the summer but are masked by the green chlorophyll. As chlorophyll breaks down in the fall, these colors become visible. Red and purple shades, on the other hand, are produced by anthocyanins, pigments that are created in the fall. These pigments are influenced by sunny days and cool nights, which trap sugars in the leaves and enhance their color.