I really like where you're going with this.

As I see it, the main issue with the saturation is that the darker shades are too saturated. I think the brighter shades are fine by themselves, but that they look washed out in comparison. In general, less light means less saturation. If you reduce the saturation of the darker shades, the brighter colors will also stand out a bit more.
Also, the dirt looks like a separate element, as it differs a lot from the grass both in hue and brightness. If you bring the dirt and grass shades closer together in hue, especially where the darker dirt shades meet the darker grass shades, they won't clash as much.

I agree that a more subtle background would be more suited for a game, and I liked EvilEye's desaturated shift towards blue, so I applied it to the darker end of the green ramp. Also pushed the darker dirt shades a bit towards green.