Why are leaves green except in the fall?

Answer 1

Chlorophyll gives plants their green colour. There are other pigments in the leaves too, such as xanthophylls (yellows) and carotenoids (yellows, Oranges and reds). These pigments are also used in photosynthesis but occur in lesser quantities than the green chlorophyll. The combinations of the different pigments make different shades of green.

Now the reason that plants look green is that they are trying to obtain energy from the sun using a particular part of the light spectrum, mainly the red and infra red wavelengths. If you remember from your physics classes the colour you see is the colour that is reflected from the object, the other colours are absorbed. So in the case of green plants, the green wavelength is reflected and all the other colours, especially reds and blues, are absorbed to drive the energy cycle in the plants.

Chlorophyll does best in the red (around 670 nm) and blue (around 500 nm) areas of the spectrum. That's why many plants have the additional pigments (xanthophylls and carotenoids) called accessory pigments that feed light energy to chlorophyll "a" from light. Chlorophyll is almost useless in the green part of the spectrum, and doesn't absorb that colour. That is why most plants are green.

Answer 2

Green is the most efficient color for absorbing light, hence maximising the amount of light captured by chlorophyll for photosynthesis.

Answer 3

because they have the green coloring pigments called chlorophyll

Answer 4

because of chlorophyll