Yes. You can change the background color by going to the Settings tab, under Advanced Resize Options.
Go to the Settings tab on the navigation menu
Scroll down to the Resize Options section
Select the aspect ratio you want to use
Click the Pen icon at the top-right:
Choose your preferred background color either by inputting a hex code here:
Click Save - the app will re-analyze your store in preparation for your new settings.
After clicking the Save button, the app will re-analyze your store in preparation for the new settings you have chosen.
Please note that this feature is only available under the 'Add Frame' resize option.