While the meat was cooking, fat dripped over and colored other leaves yellow. E ven today some people aren't quite sure what causes leaves to change color. The primary factor is the photoperiod , or the amount of sunlight a region receives during the course of a year. As the fall season marches on, the days become shorter. The decrease in sunlight intensity, shorter hours, and cooler temperatures reduce the growth and food-making processes that normally flourish during the spring and summer seasons.
Plants rely on sunlight for energy and nutrients.
The chlorophyll begins to break down as the tree absorbs the nutrients into the trunk and eventually, the roots. As this occurs, the green color starts to diminish since chlorophyll reflects green wavelengths. The yellow pigments have existed in the leaf since spring but were not visible until this point because of the large amount of chlorophyll. Now, the yellow hues are able to emerge since they last longer than the green chlorophyll. These yellow pigments are also referred to as Carotenoids .