Answer:
I'm sometimes white but most often I'm black. I take you there but never bring you back.
In buckles or lace, I help set the pace. The farther you go, the thinner I grow. What am I?
I hide but my head is outside. What am I?
I look like a tiny trombone
Use me to reward good behavior.
No matter how little or how much you use me, you change me every month.