Your problem is atm that you are working with too much outlines, while your whole textur looks really busy. The only version which has a bit of volume is the third line middle position try.
Atm your turf looks also more like a bunch of small round stones. You can change this if you are cluster more of the single planes together and work with bigger shapes to simplify the forms drastically.
It's possible to add material structure with just 2 colors, the secret is the design of the line where the 2 colors hit together. It's possible to simplify grass down to a spiky line and mud to a line made out of some circle segemnts. By adding some additional single forms you can make a smother gradient.
look which styles other games used. this is a completely different approach with just some raw forms of color.