With fall officially underway, the leaves on many varieties of deciduous trees are starting to change color in northern climes. Why? Because chlorophyll production is declining, and as a result, the leaves lose their green color and reveal their true underlying color, says SmokyMountains.com. Beta-carotene produces orange leaves, anthocyanin produces reds and flavonols yellows. To protect themselves from winter’s harsh temperatures, perennial trees cut off leaves’ supply of water and nutrients to hibernate.