Answer:
To unravel me you need a simple key, no key that was made by locksmith's hand. But a key that only I will understand.
When liquid splashes me, none seeps through. When I am moved a lot, liquid I spew. When I am hit, color I change. And color, I come in quite a range. What I cover is very complex, and I am very easy to flex.
This only turns over once you have traveled very far. What is it?
Through its wounds, water does run. It once held many but now has none. What is it?
What has four wings but cannot fly and uses the wind but does not know why?
You use it between your head and your toes, the more it works the thinner it grows.