Answer:
They are pigments that absorb specific wavelengths of light to use in the photosynthetic process.
Chlorophyll gives plants their green colour because it reflects green light and absorbs red/orange and blue/violet.
Chlorophyll a is the main pigment involved in photosynthesis, it is found in plants, green algae and cyanobacteria and is essential for photosynthetic organisms to release chemical energy however, it is not the only pigment used for photosynthesis. All oxygenic photosynthetic organisms use Chlorophyll a but can differ in accessory pigments such as Chlorophyll b
Chlorophyll b is a form of Chlorophyll that helps with photosynthesis by absorbing blue light (primarily) and is yellow in colour.
Other accessory pigments include carotenes and xanthophylls (red/orange) and phycobilins (brown)