Answer:
I usually wear a yellow coat. I usually have a dark head. I make marks wherever I go.
White bird, featherless, flying out of paradise. Flying over sea and land. Dying in my hand.
A morbidly-named body of water
I cost no money to use, or conscious effort to take part of. And as far as you can see, there is nothing to me. But without me, you are dead.
What can be swallowed, But can also swallow you?
If it’s information you seek, come and see me. If it’s pairs of letters you need, I have consecutively three. What am I?