The example was not correct, however it pointed me in the right direction.
I found a solution that involves setting the background image of the control
behind the grid (in this case the form), and then setting the following properties.
gridControl1.SupportsTransparentBackColor = true;
gridControl1.Properties.BackgroundColor = Color.Transparent;
gridControl1.BackColor = Color.FromArgb(0, SystemColors.Window);
Now the cells are opaque, but the remainder of the control displays the background image.