Leaves change colour in the autumn as light and temperature are the main factors affecting leaves. Three basic pigments, chlorophyll, carotene, and anthocyanidin, change according to light absorption and temperature.
In spring and summer, when trees are growing, chlorophyll is produced in large quantities by sunlight, making the leaves look green. In autumn, as the length of the day shortens, the temperature drops, chlorophyll production slows, some of the original chlorophyll is destroyed and photosynthesis is reduced, causing the carotene in the leaves to be unmasked and show their colours.