As the days shorten, there is less sunlight energy to manufacture food. Nutrients and minerals are withdrawn from leaves and transported to the permanent parts of trees such as the trunk, stems, and roots. Chlorophyll breaks down. But leaves contain other pigments that give them their fiery fall colors. These colors, though, are hidden most of the year by the abundance of chlorophyll, making leaves appear green.
Leaves reveal their autumn colors as chlorophyll breaks down and other pigments are unmasked.
Xanthophyll produces the color yellow, and carotene, like that in carrots, produces yellow-orange. Leaves continue to produce sugar during the day but cold night temperatures prevent trees from withdrawing the food out of the leaves. Sunny days and cool nights can produce a sugar-related pigment, anthocyanin, which produces fiery reds. Other chemicals and breakdown products produce bronze, purple and crimson. Birches, beeches and tulip poplars turn golden.