Hello Ella,
Thanks for submitting a question about changing the background color of the “Call to Action” widget. In this case, that particular style is controlled by the theme’s stylesheet and is not editable in the customizer.
You could change this by removing the default Call to Action and adding in your own Visual Editor widget. Then you could control the content in that space with more accuracy. You could even create custom CSS classes and use them in the text editor to exactly mimic the Call to Action styles (excluding “background-color” of course).
Otherwise, the more advanced option would be to use custom CSS to change the styling on the Call to Action class. This is something a front end developer could easily fix for you.
Best,
Christopher M.