Hm it says you've got 11 colors there. It seems that a few of the colors there are pretty indistinguishable from one another, especially a lot of the green midtones. That said, the colors that ARE visible from 1x are nice choices. I'd just merge a few of those, and you're on your way. Other than that, I would just add a bunch of variation tiles as Alex pointed out, and a bunch of transitions between the varying levels of grass brightness.
Good job, $ymbol.