What Am I Riddles

Question: I am almost nonexistent through sorrow, yet am frequent through happiness. I have no contact, yet I am contagious. What am I?

Question: What goes black when you buy it, red when you use it, and goes white when you throw it away?

Question: I'll bring out your bulls,
and slow your roll.
I may even come out of your skull.

What am I?

Question: What goes up when the rain goes down?

Question: Living I do not exist. Dead I am an inspiration. You always doubt me. But never reject me. I am what is given from old to young. Without me people would not learn mistakes. What am I?