Well I think the bright white sky is just fine and works well for the effect you're looking for!
The lighting, composition and models are very good. In overall great work so far.
However, I've 2 suggestions for improvement:
First, to make the grasses look better and to get the more photographic look you might consider rendering it with higher AA settings and maybe also up the detail setting a bit.
I don't know which GI settings you use, if you didn't render it with at least GI 2/2 you should definitely do it. But as far as I know you, you probably have done that

Second, the tree on the left is a great model, however I'm not fond of the bark-texture. It's scale is way too big. I think a bark with smaller texture scales will look much much better.
You might try using these I've posted a while ago:
http://forums.planetside.co.uk/index.php?topic=3693.msg38179#msg38179If you like the results I can send you the full-res versions of the textures.
Hope this helps so far.
Martin