Autumn leaf colour affects the normally green leaves of many deciduous trees. In the autumn season, leaves taken on various shades of red, yellow, purple, black, orange, magenta, blue and brown.
But why are leaves normally green? Most leaves look green because photosynthesis, the mechanism used to produce sugars to provide the energy for all of the tree’s processes relies on chlorophyll, and chlorophyll is driven by blue and red light. Therefore it is the green light that is left over to be refelected or passed through the leaf and therefore most leaves appear green.
Some green leaves have other pigments in the leaves that mask the green colour produced by the presence of chlorophyll, such as copper beech.
In autumn, when deciduous trees start to lose their leaves, the chlorophyll is broken down and moved from the leaves into the woody structure. This is why the yellow pigments normally found in a leaf but masked by chlorophyll now show through – a similar process which happens with the ripening of a banana.
Red pigments mixed with yellow in different proportions produce oranges, reds, purples and sometimes blues. The red colours are produced in dying tissue from sugars that remain in the leaf.
The Forestry Commission provides a list of excellent places to catch the last of the autumn colours http://www.forestry.gov.uk/forestry/autumntop10 – top of the list is Westonbirt Arboretum!