Caretenoids appear yellow-orange since they absorb light in the blue/green wavelengths reflecting back the orange/yellow wavelengths. . Production of carotenoids begins in the spring. Since that production is not dependent on the level of sunlight, it continues into the fall.
So, why don’t most leaves have a yellow or orange tint during the growing season? Simply stated, it is because their colors are masked by chlorophyll pigment which begins production around the same time in the spring. The yellow or orange color only becomes visible in the fall as the chlorophyll is resorbed by the trees. If, however, there is a superabundance of carotenoids, the leaves may stay a yellower-green.
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