Answer:
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.
I cannot be felt, seen or touched. Yet I can be found in everybody. My existence is always in debate. Yet I have my own style of music.
Only two backbones and thousands of ribs.
By the way, what never moves, wears shoes, sandals and boots, but has no feet?
I'm not really more than holes tied to more holes. I'm strong as good steel, though not as stiff as a pole.
I am your mother's brother's only brother in law. Who am I?