Most people know, at least in broad brush strokes, HOW? autumn leaves turn out to be so colorful. I was wondering WHY? and Why so many colors? Just to clear up the HOW? part... At the most general level, when the weather turns colder, deciduous (leafy) trees stop making green pigment and the remaining underlying colors are revealed. More specifically, as the in the late summer, the veins in leafy trees start to constrict and the production of the compound responsible for photosynthesis, chlorophyll, is down regulated through the reduction of a single protein FtsH6. As the chlorophyll synthesis is reduced, the remaining chlorophyll is converted to a colorless set of compounds called NCCs (nonfluorescent chlorophyll catabolites) As the chlorophyll ebbs, three specific pigments are revealed: Carotonids are the yellow and orange colors in leaves. They are present all year long and concentrated in structures called plastids. Note that this is a class of compounds and lots of the yellow co