Leaves are basically food-making machines. They are able (through photosynthesis) to turn water, carbon dioxide and sunlight into a nutritious substance called glucose, which in turn provides sustenance for plants and trees. The leaves use a green pigment, chlorophyll, to aid in the photosynthesis.

But as the days shorten and leaves absorb less light, trees prepare for autumn by stopping the food-making process. Consequently, the production of chlorophyll drops off, turning some leaves orange and yellow in the fall.

Colors, like yellow and orange, are in leaves all summer, but the powerful green chlorophyll overwhelms them.

	The production of red pigments indicate that the leaves still have food trapped inside; brown pigments are produced by the waste material left in leaves.
	During the summer, leaves make more glucose than the plant needs for energy and growth. The excess is turned into starch and stored until needed.

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