Water is most transparent in the middle of the "visible" spectrum (green). It absorbs red and scatters blue. The atmosphere has a lot of water as does, of course, the ocean which was the birth place of plants and eyeballs.
It would be natural for both plants and eyes to evolve to exploit the fact that there is a green notch in the water transparency curve.
Edit: after scrolling, I find more discussion on this below.
I think any explanation along those lines would have a "just-so" aspect to it. How would we go about verifying such a thing? Perhaps if we compared and contrasted the eyes of savanna apes to forest apes, and saw a difference, which to my knowledge We do not. Anyway, sunlight at the ground level peaks around 555nm, so it's believed that we're optimizing to that by being more sensitive to green.
