Scientists already know why plants are green (Score 4, Informative)

It's pretty obvious once you know the argument. It's due to light-scattering. There's so much energy in the sky all day that it doesn't matter what color you absorb, there's plenty at any visible wavelength. But during sunset and sunrise there's predominantly red light in the sky, and a green plant would be more efficient at absorbing red light (they're complementary colors) than if the plant were another color. This blog entry goes into it:

http://blog.myspace.com/index.cfm?fuseaction=blog. view&FriendID=187945&blogMonth=9&blogDay=24&blogYe ar=2006