Chlorophyll and accessory pigments
When leaves turn colors in the fall, they are actually just revealing the pigments that have been "under there" all along, but the green chlorophyll pigment dominates in land plants, but it is one of the first chemical to begin to deteriorate and break down as daylength shortens (more so than the seasonal temperature changes).
Chlorophyll pigment absorbs light in the yellow-orange as well as the blue-purple wavelengths, thus our eye perceives the reflected color of green.
Carotenoids and xanthophylls absorb in wavelengths that generally don't overlap the wavelengths preferentially absorbed by chlorophyll a and b. So we perceive a different color of reflected light bouncing off the plant whose accessory pigments haven't completely broken down.