At the same time, surging sugar concentrations cause increased production of anthocyanin pigments. Leaves containing primarily anthocyanins will appear red. Carotenoids are another class of pigments found in some leaves. Carotenoid production is not dependent on light, so levels aren't diminished by shortened days. Carotenoids can be orange, yellow, or red, but most of these pigments found in leaves are yellow. Leaves with good amounts of both anthocyanins and carotenoids will appear orange.
Leaves with carotenoids but little or no anthocyanin will appear yellow. In the absence of these pigments, other plant chemicals also can affect leaf color. An example includes tannins, which are responsible for the brownish color of some oak leaves.
Temperature affects the rate of chemical reactions, including those in leaves, so it plays a part in leaf color. However, it's mainly light levels that are responsible for fall foliage colors. Sunny autumn days are needed for the brightest color displays, since anthocyanins require light. Overcast days will lead to more yellows and browns.