Final answer:
Leaves on a tree are green because of the pigment called chlorophyll a, which absorbs blue and red wavelengths but not green. Other pigments in plants also contribute to the overall green color of leaves.
Step-by-step explanation:
The leaves on a tree are green because of the pigment called chlorophyll a, which absorbs wavelengths from either end of the visible spectrum (blue and red), but not from green. Since green is reflected, chlorophyll appears green to humans. Other pigments in plants, such as chlorophyll b and carotenoids, also contribute to the overall green color of leaves.