@Turrican: Thank you, definitely now i'll play more with layers distance, and fog color/distance to get good effect. Example that you gave me is great, desert level in Trine looks perfect. I miss this addition, but i found something interesting in one level where we can see over 50% of blue sky on screen, beacuse the biggest problem i have with the background on the places where we can see the blue sky. In Trine i see some details are painted in sky layer, like bluried mountains. Maybe is point, paint some fog color and some very bluried mountains in Skycube to get better transition with lastlayer. Btw if i put image instended of skucube i do not know did there are some engine function or shader, where we can control strenght and position of fog on this sky image, i never try this, but this also might work. Or simple ignore fog on this layer and make fake fog effect in Photoshop.

About our desert level, yes i already have some tumbleweeds, heathaze, dust,... all models and concept is there, i just need put this in level, beacuse this is last part of game and has not yet come on the order for polishing. Trine desert level will give me new inspiration .

Here is one picture with forest. I thinking about bacground image and fog color