After examining a handful of real life terrains and how grass grows on them, I've learn that a terrain is composed of different types of grasses. You have freshly grown, young grass, but in some areas you have older which is slightly darker. In some areas, where the sun shines a lot terrains tend to have dead or yellowish/burnt grass.
It became obvious that I need to combine several types of textures and paint them logically over my terrain.
Same attention went to all the other textures, here are some of them: