What chemical changes cause leaves change color in autumn?
The dying of chlorophyll due to the changes in the weather.
Chlorophyll is the pigment that gives vegetation its green colour. Only plants that are green have chlorophyll. These plants have red, yellow and orange pigmentation, but is usually masked by greater amounts of green.
In the fall, due to the changes in temperature and changes in the daylight length, the leaves stop their food-making process (photosynthesis). The chlorophyll breaks down - the green colour disappears. This results in a clear, identifiable colour of red, yellow, orange and occasionally brown.
There are many factors that affect colour: temperature, light, and water supply. A lack of all results in the change. Remember that these are factors and must all be deficient in the plant for the colour change to occur.
Special species of trees called conifers, maintain their green colour due to their special adaptability to the cold.
Hope this helps :)