Why are plants green? Photosynthesis & Chlorophyll
Substances on earth gain their colour depending on how they absorb light. Anything that is poor at absorbing light on the green portion of the electromagnetic spectrum, appears green to the human eye.
A plants substitute for eating is called photosynthesis. Plants use light energy from the sun, along with Carbon Dioxide and H2O to create sugars. It is the substance called chlorophyll; responsible for photosynthesis, that causes plants to be green.
Because plants need sun light to photosynthesis, they must collect it efficiently. They do this by sprouting leaves from their stem or trunk. The leaves are full of chlorophyll required for harvesting sunlight. Chlorophyll absorbs blue light well, followed by red light. It is exceptionally poor at absorbing green light. As a result, the leaves of plants, or anywhere there is a substantial amount of chlorophyll; appear green to human eyes. The darker the green, the heavier the concentration of chlorophyll.