How do I make different regions different background colors?

This is probably pretty simple and right in my face but I can't seem to figure it out or see where to do this at.

I have a small region on one of my pages that I want to stand out a bit by changing the background color of just that one little region. I looked through the settings, etc, but I don't see how to do this.

I'd greatly appreciate a point in the correct direction! Thanks!