How do I change the background color of a chart?

You can adjust the background color of what we call the graph area, the area within the axes where your series are graphed.

Click on the graph area background (avoid the graph itself and the grid lines), and open the Presentation properties tab. In the Appearance group, you can select the color from the drop-down list or create a custom color.

If you want to re-use the selected background color often, you can pin it to the drop-down list or save it in as part of a style sheet that you can easily apply to your charts.