Final answer:
Fall leaf coloration in deciduous trees occurs due to the cessation of chlorophyll production, allowing hidden accessory pigments to become visible.
Step-by-step explanation:
Fall leaf color on deciduous trees is primarily a result of the cessation of chlorophyll production, which allows the accessory pigments to be revealed. As the days become shorter and the temperatures cooler, the production of chlorophyll slows down and eventually stops. This decrease in chlorophyll allows the accessory pigments, such as carotenoids (yellows and oranges) and anthocyanins (reds and purples), which are present in the leaves year-round but masked by the green chlorophyll, to become visible and give the leaves their autumn colors.
While chlorophyll is the main pigment responsible for photosynthesis and the green color of leaves, the accessory pigments have their own roles, including supplementing chlorophyll absorption during the growing season. When the amount of daylight decreases in autumn, the change in the environment triggers deciduous trees to begin the process of nutrient recycling and prepare for the upcoming winter by breaking down and reabsorbing nutrients from the chlorophyll, which leads to the revealing of the brilliant fall leaf colors before the leaves are eventually shed.