Hey! Thanks, glad you like it!
As for the grass, the darker shades are better to be used for places where you need a shadowier/darker place. Or like a focusing/composition tool. Make the places that are not as important darker, while keeping your main paths, and other spots where you can walk lighter. Stuff like that, if that's what you meant.
Or if you meant how to get the light grass transition to darker grass, you can just use layers. Keep the lightest grass as base layer, and add the darker shade on top on another layer. However i included also the tiles which have integrated dark to light colours, which you can use on the same layer.