The display background can be filled with a single color or with a color gradient.
Click the One Color button to fill the background with a single color. The background color can be changed by clicking on the colored box which shows the currently-selected color. This will display a color selection dialog from which you may select a new background color.
When you are happy with your color selection, press Ok in the color selection dialog. The color will be updated in the colored box (and in the Preview Monitor, provided no Wallpaper is selected).
To fill the background with a color gradient or pattern, click the Two Color button. A second colored box will appear. Click on this box to select the second color. Now click on the Setup button to choose how to blend the two colors. A dialog and Preview box will appear. You may choose to progressively blend the colors from top to bottom of the screen, from right to left, or in a pattern selected from the list shown. You will see a preview of the choice you make before you apply it. Click OK or Cancel to leave this dialog.
A blend of the two colors uses only 8 colors, leaving plenty free for other applications. However, it requires an image the size of your display to be maintained in memory.