Wrong. It has nothing to do with the temperature...it's all the shortening day lengths in fall. After living in Vermont for years, I had to learn all about it, since Vermont claims to have the most beautiful fall foliage in the world. There is only one place in China with the same collection of tree species (heavy on sugar maples) that rivals Vermont's color. At least that's what Vermonters say. This photo is in Colorado, and while the species are different, the fall glory is much the same.
I was amazed to learn that the bright pigment of the fall leaves (reds, yellows, etc.) is there throughout a leaf's life, but until fall, all the various colors are covered with green. That's because the tree is producing chlorophyll masking the true colors. As soon as the days get shorter and shorter in fall, the chlorophyll production shuts down, and the true color of each leaf in the forest is revealed.
If you live in a big foliage color area like Vermont, you love the leaves and crisp fall days. There may be nothing more beautiful in nature than a stately maple tree in full color, backlit by bright afternoon sun. But there is always a dark side. Because as the fall colors glow, you know that in just a few weeks (around the end of October) you're going to be suddenly looking at bare trees and dreary winter skies. From the most magnificent scenery and weather of the year, you are suddenly plunged into the most depressing period of all. Almost everyone thinks January, while really frigid in Vermont, is usually a spectacle of snowfalls, which bring their own beauty. But November is all bad...cold rain, no sun, and general gloom--the price paid for nature's big fall show. One has to simply trudge through it, until the brightness of the holidays lifts all spirits.