Chlorophyll is the molecule that traps the energy of the sun and is called a photoreceptor. As summer ends and we start to move towards fall, the days start getting shorter. Pin On Best Of Seasonal Family Fun The plants can reabsorb the molecules that make up. Why do leaves change color in the fall biology . Changes in these weather conditions can play a role in how early the leaves change and how long they keep their beautiful colors. Trees start building a protective seal between leaves and their branches as the weather turns. Weather is also an important part of the color change. There is so much chlorophyll in an active leaf that the green masks other pigment colors. Leaves change color in fall because the green pigment breaks down exposing the yellow and orange pigments that had been hidden. In the fall, the temperatures get colder and there is also more rain and snow. There are two theories according to jennifer wells, leaf color change:. Leaves change color