Story Layout Question.

So I'm floating around Mibba, trying to figure out how to work the new mibba. (If you've seen any of my previous posts, you will quickly learn how hopeless I am with technology. Which is very...)

Anyway, I was trying to make a new story layout. How do you change the background's color. I tried writing what I wanted and doing a code.

Help would be appreciated very much.
-Sofie