I've used a couple of Distance Shaders, one on Near as a blend of the Power Fractal Shader that shapes the foreground knoll, another on Far applied as blend on the Strata & Outcrops Shader that shapes the rugged background mountains. On my first render of this scene (which I uploaded on the Renderosity site) the Sweet Birch trees appeared too dark for my liking. I found the Diffuse Colour on the leaves tiff at 0.5 (mid-grey) so adjusted it to 1 (white), and that made a difference. I also added a couple of Light Sources over the trees; one to slightly brighten the trees on the right sunny side of the knoll, the other Light Source I had on a negative strength to slightly darken the trees on the left shadier side of the knoll. This lighting adjustment, along with adding a scattering of young birches, I think help to increase the sense of diversity among the one species I've got here. On Bob's (Chroner) advice I've given the grass more colour variation on this re-render, and increased the Displacement Roughness on the knoll. I may have gone a bit too far with the latter as the rockiness has overtaken the grass too much.
I like the mountains and the foreground rocks. The color of the trees (a problem I'm dealing with as well) and the grass are off. I like the use of the distance node on the background.
I'm sure your right with the colours, especially the grass. It doesn't help that I'm colour blind with reds and greens (I always fail those stupid colour blindness tests, you know, the number (that I'm sure isn't there) in the spots). Maybe some kind soul will give me a sample of neutral (neither in sun or shade) grass colours that I'll use as a reference.
I'm still working on a good grass color, but maybe someone here will give you (and me ;D ) the RGB values for a decent grass color. There have been a few around here.
I found it helpful to take the color values from photos
as a starting base when i began working with terragen. ;)
the grass could use more work!...I like the mood in this one....