You can also use the Color Tool to set the background color. By default, the first color will be set to the background color. To change it, select a new color and chose Set BG Color from the drop-down.
Changing the background color will tell the game what color to use when clearing the screen and what to default to when a color is out of range. The background color will display a special icon in the Color Tool making it easy to identify which color is set.