Answer
Green light, because it is not absorbed by the photosynthetic apparatus and, so, cannot power
Work Step by Step
Please see Fig. 10.10, which shows the wavelengths of light which can power photosynthesis. Note that there is a valley (non-absorption) in the green wavelengths and for some, but not all, yellow. If light is not absorbed, its energy cannot power photosynthesis. Consider that the color we see is the wavelength most reflected by the pigment and least likely to be absorbed.
