How to change the color of the checkbox?
Frequently Bought Together allows you to easily customize the color of the checkboxes to better match your theme.
To do so, please open the app preferences page and navigate to the Visual styles → Checkbox.
There you will find an option to customize the background color, as showed below:

You can easily select your preferred color using the tool showed below, or you can copy the color name/code.

Lastly, please remember to click on Save, so that the changes can be successfully applied.