Title says it all, need help changing the background color of the shoutbox.

Have you tried to change

Language: CSS
#shoutbox {
  height: 350px;
  overflow: auto;
  width: 100%;
  border: 1px solid #979ea1;
  border-radius: 3px;
  margin: 0 0 1em;
  padding: 0.5em;
}

?
You find that in the folder content/page_style.css ?