South Texas is typically one of the last places in the country to see the leaves turn. SAN ANTONIO — Now that the clocks have been set back, fall temperatures are on the way and thanks to the expected temperature drop, fall foliage is also on the way. During the spring and summer, leaves are typically a vibrant green. The green pigment is due largely in part to chlorophyll, a key ingredient that allows plants to absorb sunlight and convert it to usable energy.