This is a complicated subject. Factors which are involved in development of fall color include the genetic capacity to develop the colors, proper growing conditions and location, and the absence of leaf diseases. Development of autumn color really means that the chlorophyll in the leaves has degraded and the underlying colors hidden by the green become revealed. Yellows were there all along, sometimes purple is present throughout the growing season as well, and is apparent as dark green leaves until the chlorophyll degrades. Then the purple remains.
Reds often develop in the autumn under the influence of sunny days.
The sunny days allow the plants to produce sugars. The cool nights prevent the movement of sugars from the leaves to other parts of the plant. The sugars accumulate in the vacuoles, storage organs in the cells, and are converted to anthocyanin and other pigments. When the green chlorophyll degrades, these stored pigments become visible. Genetics, or the innate ability of a plant to develop fall color is important.