In Boutique, the editor background color gets switched to whichever color is set in the Customizer ➤ Background.
This doesn't reflect how the theme renders the page's background color, though. It makes it so the editor is dark (if set to a dark color), but the actual published page is always white:
In Boutique, the editor background color gets switched to whichever color is set in the Customizer ➤ Background.
This doesn't reflect how the theme renders the page's background color, though. It makes it so the editor is dark (if set to a dark color), but the actual published page is always white: