Answer:
The more you have of it the less you see. What is it?
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.
My full powers come when my makers are dead. I await a heavy hat to put on my head. What am I?
The warmer I am the fresher I am.
I am all around you but you cannot see me. I have no throat but you can hear me. Valued during summer but despised in the winter.
Black we are and much admired. Many seek us if they are tired. We tire the horse, and comfort man, and turn White when we've fulfilled your plan.