Thanks for allowing me to dl. Do you create the 2nd two layers (grey layers) yourself as well? How do you decide how those two layers should appear? I'm assuming a lot of trial and error, and experience. Are those grey layers available in any of the resource links provided?
I created the grey layers myself - they are grey because I made them grey, btw, they might as well be colour. But to me they are effect layers and making them b/w helps me remind myself of it: The detail layer I made my importing several lawn/grass textures from the public domain, combining them into one continuous patch of even grass, making it seamless, then using the Level adjustment to bring out the bright and dark bits slightly better. The normal map I made from another grass texture I got from textures.com, applied a bit of filter magic as well, such as render clouds and Reticulation (Tipp: Filters > Others > High Pass is extremely helpful for texture creation).
With time and mileage I developed a bit of a visual anticipation of how they would contribute to the end result. Yet there always is uncertainty: What may look great in Photoshop may turn out to be an epic fail in CF. As you say, trial and error is the only way to find out what's what.
I understand why certain, very keen yet computer graphics-illiterate members would want reassurance that they will not need to go into texture creation themselves and can get all they need from the public domain. Well... you should be okay and if you look long enough you should find all that you want. And if you are willing to pay for dl's of high quality stuff, no worries at all. But no pain, no gain - DIY textures are always a bit more special imo, and since they are one of the most vital parts of course design, this is where you can, as a designer, gain a lot more control over the look and feel of your work.
But that's just how I roll, so don't fret. Most players are utterly oblivious to the finer points of texture making and CF, they keep proving this in their reviews, and as long as it looks green and grassy they will be happy. If you start your CF adventure, play to your strengths and don't bother about your weaknesses, just design with passion and put in the (many) hours - and you should be okay.