Another problem with these tiles, is that they are a ramp of full-sat green; when applying shades, it helps to think of where the setting takes place.
Is it in a jungle, forest, or maybe in a park? because once you figure out where your tile is, it will help you figure out what colors to use in your ramp,
and how saturated those colors become; with the "generic" grass tile, it takes place in (I'm guessing) a park, on a sunny day.
Parks have nice cut grass to walk on, as well as some bushes and longer grass to look at. We also know that, when the sun is out,
all of the highlights get tinted a nice, but not too noticeable yellow; while in the shadows we can sometimes make out a little bit of blue
because of the second-most prominent light source, the sky! the only way grass could be only green would be if all of the light sources were green too.