Chlorophyll is the pigment used by all plants for photosynthesis. There are two versions, chlorophyll a and chlorophyll b. These are structurally very similar to one another but have different colors, blue-green and yellowish green, respectively. Both pigments fulfill different jobs during photosynthesis and are therefore bound very selectively by the proteins of the photosynthesis apparatus in plants. But it is still unknown how these plant proteins recognize the two chlorophylls and thus bind them selectively.