The Science behind the Autumn Colors
Every autumn across the Northern Hemisphere, fading daylight hours and falling temperatures induce trees to prepare for winter. In these preparations, they shed billions of tons of leaves. In certain regions, such as our own, the shedding of leaves is preceded by a spectacular color show. Chlorophyll is located in organelles called chloroplasts in the cytoplasm of plant cells and gives leaves and other plant parts their green color. Chlorophyll absorbs red and blue light from the sunlight that falls on leaves. Therefore, the light reflected by the leaves is diminished in red and blue and appears green. Light regulates chlorophyll production, so as autumn days grow shorter, less chlorophyll is produced. As time goes on the green color starts to fade from leaves. (http://www.butler.edu/herbarium/fallcolor/leaveschange.htm)
Carotenoid pigments are responsible for the yellow and orange colors in leaves. Carotenoids are located in the chloroplasts and assist chlorophyll in the capture of sunlight for photosynthesis. Carotenoid production is not dependent on light, so levels aren't diminished by shortened days. Like chlorophyll, carotenoids absorb energy in the form of light and aid in photosynthesis, they just do it to a much lesser degree, and by absorbing different wavelengths of light; carotenoids absorb light at blue and blue-green wavelengths, so the light that they reflect appears yellow. (http://chemistry.about.com/od/howthingsworkfaqs/f/fallleafcolor.htm)
Anthocyanins are responsible for the pink and purple leaves. Anthocyanin pigments are formed when sugars combine with complex compounds called Anthocyanidins. Anthocyanins absorb blue, blue-green, and green light. The light they reflect therefore grants them an incredible scarlet, or purple, hue. As fall sets in, certain trees like red maples and sumac crank their anthocyanin production up, causing them to appear particularly red. Some say that anthocyanin...