Red light is the most efficient monochromatic spectrum for plant growth. However, all the colors have functions. If a person were especially good at hearing bass sound, that means the other pitches should be emphasized, so that one could hear the whole melody. For light to be efficient for plant growth, it must be full spectrum with close to equal linearity and amplitude through the production of 400-700 nm, with a slight bump in the red.

One guys opinion, but real close to what I've been saying.

New Technology for Plant Lighting

good reading