This link is a little gem that any science fiction writer should hold on to. It tells you what color the plants should be in an extra-solar system. The logic seems to be simply that plants absorb the light that is most readily abundant, and chlorophyll reflects green because there is less of it (after absorption by the atmosphere).
The article suggests that only yellow, green, and red plants are to be expected. It did not detail why. In fact, this article from Astrobiology leads me to think purple should be in the game. In fact, another theory supposes that the earth was covered with purple vegetation.
Astrobiology is, I think, a must-read website for science fiction authors.
Another question I have is whether brown plants make sense. The idea is that the would actually contain melanin, the pigment that makes human skin dark. Since the article cited proves that it is possible for fungus, why wouldn’t it work for other types of plants?
Some even believe that alien plants may be black.