Plants are green because of a pigment called chlorophyll. Chlorophyll absorbs all colors of visible light except for green, which is reflected. Thus, the reflection of the green part of visible light is what causes plants to look green.
Organelles called chloroplasts contain the pigment chlorophyll. Photosynthesis is the process of making food out of carbon dioxide, water and sunlight. All organisms capable of performing photosynthesis, except for the photosynthetic bacteria, contain chlorophyll. Two types of chlorophyll exist in green plants, with the most prevalent being chlorophyll-a. Chlorophyll-b also occurs in all plants, but in smaller amounts than chlorophyll-a.
Other energy-absorbing pigments also exist in plants. Carotenoids, the pigments that give carrots and fall leaves their orange color, absorb all colors of the visible spectrum except for orange, while lycopene gives tomatoes their red color.