While I do not know much about aquatic plants/botany I do know that in general plant leaves have two different types of Chlorophyll, types a and b. Each has an optimal absorption region at different wavelengths. Now if your bulb has a majority of the energy distributed in regions outside of these wavelength regimes, the plants would have to "work" harder to utilize the light energy for photosynthesis. I guess it is plausible that they could manufacture necessary pigments/chemicals so as to be able to utilize the light that they receive. This could very well also possibly cause a difference in appearance, but I am not sure if this is actually the case.

This article : http://www.aquaticplantcentral.com/f...osythesis.html

has some useful information, although I do not really know how scientifically accurate it is.