Answer:
It's anything but amusing when this body part gets hit.
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.
Where do you go in through one hole and come out through two holes at the same time?
This is needed both for courage and hardcover books.
Alive without breath, As cold as death, Clad in mail never clinking, Never thirsty, ever drinking
I stay where I am when I go off. What am I?