As the days turn longer, less sunlight means less oxygen and glucose for plants and leaves and ultimately less chlorophyll, which hides the reds, yellows and oranges. Different materials cause different colors in leaves. Red comes from glucose, brown from waste and purple from anthocyanin. Yellow is always present in leaves, but during spring and summer, the green overpowers it.
The timetable for leaf transformation runs from September through
early November. Typically, the first to see breathtaking fall
foliage are the Rockies, Upper Midwest, and New England. From there
leaves begin to change further south into the Ohio Valley, Pacific
Northwest, and Middle Atlantic toward mid and late October.
The first frost and time of leaf change typically go hand in hand.
Within a week or so of the first frost, expect quick leaf
transformation. Other factors such as the amount of water during the
summer and early fall impact the full potential of color. More water
means better color.