Yeah, it was only a matter of tweaking 3 files so it went pretty fast. Best tweak suggestion I can give you is just play around with each file individually, then test and see what happens. Darkening the grass-b file will darken all of the grass textures at once. I used small Curve adjustments on that one, but you can try just a brightness adjustment. Or darken the sbancamento_C texture which I think only impacts the level of the brownish areas. I added a little bit more green to that texture which is why things don't look so brown. Not exactly sure what the grass-mask_NEW file does exactly because I never did test that one by itself. I know from past track skins i've done that lowering the brightness on the mask does lower the brightness of the grass. Give it a try and see what happens. Now you got me curious. Think i'll go do some experimenting.
There's actually another grass texture involved in the mix, but I didn't adjust that one so it's not included. It's the one for the green grass areas.
EDIT: Yes, lowering the brightness on the grass-mask_NEW file will lower the brightness on the grass. I'd say try that one first. Don't know what program you use, but trying going -5 on the brightness slider. If you want a little more saturation, you could also do a slight saturation increase on the grass-b file. Again, go in small steps. Here's what I came up with. I think it fits in with Shi's original intended look by keeping some hint of a dried out look, but isn't as off putting as the original grass.
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