Flogging a dead horse, perhaps, I still find that not only is the contrast still too low, but the lighting is also inconsistent.
Shadows indicate that the light source come directly from the top, yet the croc is darker on his left side.
Now, I don't actually care about that since the shadows are so basic and symbolic.
What I do care about, though, is that only the croc has a darker side. Everything else in the game should too, both objects and the landscape.
If you add that, it will also probably bump the contrast all by itself.
Since you learned Blender for this, may I ask if you are planning to learn OpenGL by yourself too?
I'm also an iPhone owner and want to make an app of my own some day, though I will probably not start with an OpenGL one...