Really enjoying this thread, but in my opinion you definitely need some variation in that grass colour. Perhaps some areas where it isn't so lush, I'm thinking some brownish patchy areas where the sun has scorched grass. In future you might want to include some more of the scorched grass colour in your mix.
I know it might sound drastic, but hacking it with scissors then giving it a light blast with the airbrush with a light dirty colour might help just to pick out the tips of the grass where it is slightly dying back.