How to change the background color

The background color is set from Plot->Layout->Edit…. Select the tabs as shown below (Chart->Panel->Gradient) as shown below.

Now you can change the colors. In the example above, the gradient starts with white and ends with blue. The results is as shown below.

If you do not wish to use a gradient, make sure the check box shown below is not checked

Then select the Background tab as shown below

In the example above, the selected color is white. Click the Panel Color… button to change this.