It is difficult to focus on one individual leaf when you are confronted with walls of color. The intensity of the Fall colors depend on subtle differences in temperature and the length of daylight. According to the State University of New York College of Environmental Science and Forestry these changes are caused by the breakdown of the chlorophyll in the leaves. To quote from this article,
But in the fall, because of changes in the length of daylight and changes in temperature, the leaves stop their food-making process. The chlorophyll breaks down, the green color disappears, and the yellow to orange colors become visible and give the leaves part of their fall splendor.
At the same time other chemical changes may occur, which form additional colors through the development of red anthocyanin pigments. Some mixtures give rise to the reddish and purplish fall colors of trees such as dogwoods and sumacs, while others give the sugar maple its brilliant orange.
The autumn foliage of some trees show only yellow colors. Others, like many oaks, display mostly browns. All these colors are due to the mixing of varying amounts of the chlorophyll residue and other pigments in the leaf during the fall season.Hmm. for some reason understanding all that does not increase the pleasure of looking at the beautiful colors.