The color of a leaf is a dance as one molecule exits and others make their way to center stage.
A leaf might seem very simple, but inside it is a chemical factory. Inside the leaf is chlorophyll, a green molecule, which trees use to turn sunlight into energy to grow.
Leaves act just like a factory. In it, one thing goes in and another thing comes out. Leaves take in light from the sun, carbon dioxide from the air, and water from the soil and change them to make sugars and starches. What goes in is sunlight, water, and carbon dioxide; what comes out is energy.
At the heart of this factory is that green chlorophyll molecule, which is working hard during the hot days. However, as the temperature drops at night and the amount of sunshine lessens, the trees know it is time to shut down for the winter. The chlorophyll in the leaves starts to break down and the green color starts to exit the leaf.
One secret about leaves is that hidden underneath the green molecule are other molecules that make the colors of yellow and orange. As the temperature drops, these colors are revealed. As for the reds and purple colors in leaves, they come from other molecules that the tree starts to make as the cold temperatures kick in.
Some years the colors in trees are bright. Other years they are dull. The best conditions for maximum color are cool days that are dry (but not too cold). If there is too much rain or wind — like during a storm — the fall foliage will not be ideal since leaves will fall off the trees. Also, an early frost makes the colors less bright. Interestingly, the colder it gets the redder the leaves will be, since the molecule that makes red prefers the cold.
So as you can see, fall foliage is a delicate dance of molecules. It only happens for a short time. So enjoy the fall colors and all that beautiful and vivid chemistry at work.