There is a nice transition between the brown and the green one, but the other seem to be not alright. I played around with the values, but didn´t get a useful result. Maybe you can tell me, how that mix-function works.
I made a mistake you should invert the color col0,col1 instead of col1,col0 and so on...
The mix function is a GLSL function blending the color with an alpha value.
Okay I get it 1/90 = 0.0111111f and I forget the 0 after the point.
Also I suggest you to make some change for exemple for the snow and the ground, if you want quick reponse comme to the irrlicht irc channel : #irrlicht at irc.freenode.net