With Amble, you can set your page to be boxed or full-width. With the full-width option, your main content will stretch edge-to-edge with no page background showing. With the boxed layout, you can centralize the main content while showing the page background colour (or image).
As referenced in the Customize your page background tutorial, using the boxed layout will allow you to see the page background.
- Go to Appearance > Customize > Layout Options
- Look for the Full Width Layout setting.
- Toggle the button to enable your page to be full width, otherwise, you can stay with the default Boxed layout.
- Click the Publish button.