Chlorophyll gives a green colour to plants. During winter, there is not enough light for photosynthesis. So they use food, which is stored in summer. As the green chlorophyll disappears or fades away, we begin to see yellow, orange and red colour. We cannot see them in summer, because they are covered by the green chlorophyll.
But in autumn or fall season glucose trapped in the leaves, after photosynthesis stops. Sunlight and cool nights of autumn cause the leaves to turn this glucose into a red colour.
It is the combination of all these things, that make the beautiful colours, we enjoy in the fall.
