Actually, they do use green - they're more reflective in green than red/blue, but it's still mostly absorbed.
Apparently at high illuminations you want to be using green too - the issue is that red and blue are absorbed so well that they don't make it past the surface of the leaf and thus the plant quickly maxes out on them, while green light penetrates further and thus reach more tissue.
So when you see pictures of leaf greens being grown under purple light - that's because leaf greens actually need less light than other vegetables, you probably wouldn't want to do that with other crops.
Apparently at high illuminations you want to be using green too - the issue is that red and blue are absorbed so well that they don't make it past the surface of the leaf and thus the plant quickly maxes out on them, while green light penetrates further and thus reach more tissue.
So when you see pictures of leaf greens being grown under purple light - that's because leaf greens actually need less light than other vegetables, you probably wouldn't want to do that with other crops.
IANAbotanist