Answer:
What is black when you buy it, red when you use it, and gray when you throw it away?
I am like thunder in your cranium
What gets wetter as it dries?
I am lighter than the material I am made of. You see parts of me but more of me is hidden underneath.
I'll bring out your bulls and slow your roll. I may even come out of your skull.
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.