In many parts of the world, trees turn red, orange and yellow in autumn. It may look as if the trees are adding new colours, but most of these colours were there all summer.
Leaves are green because they contain chlorophyll, a substance that plants use to make food from sunlight. In summer, there is so much chlorophyll that it hides the other colours. Yellow and orange substances are also in the leaf, but we cannot see them.
As days become shorter and cooler, the tree stops making chlorophyll. The green slowly disappears, and the yellow and orange colours finally show. Some trees, such as certain maples, also make a new red substance in autumn. Scientists think this red colour may protect the leaf from strong sunlight while the tree takes useful materials back from it.
Weather affects how bright the colours are. Sunny days and cool, but not freezing, nights usually produce the brightest reds. So for a beautiful autumn walk, you may need a little luck as well as a good map.