If water is clear, then green will will attract zooplankton from a greater distance. If the water is turbid, then red is likely to give better penetrance, but will not attract the plankton from as far away as colors on the more green (shorter wavelength) side of spectrum when water is clear.
I have been using black lights (blue colored to UV) to attract flying insects better than other colors, but such light sources penetrate even clear water very poorly. They make the water appear milky close to light source.
