Imagine a red dwarf star orbited by a considerably Earth-sized planet in the star's habitable zone. Assuming the planet has a sufficiently powerful magnetic field to protect its surface from the star's radiation, and life thrives on the world, what would be the most efficient pigment for plants on that world to evolve?
Assuming that other variables are Earth-like, I would say: Black.
The colour of the plants we see is not the colour of the light used for photosyntesis. The light used for photosyntheses is absorbed (*), the pigment reflects the light that is useless for the plant.
In a red dwarf, I would expect the light arriving to have a very weak green component, so almost no light would be reflected by the leafs.
Additionally, I would expect a planet orbiting a red dwarf to be "cooler" than Earth, so a black leaf would help keeping the plant warm by absorbing most of the energy from the light.
Of course, evolution sometimes takes some curious paths, so other solutions would be possible. Maybe the plant wants to show more bright colours to attract insects to polenize them, or maybe black makes them too easy to be noticed by animals feeding on them, forcing variations from the initial solution.