WP Term Images/Colors -> Advanced Custom Fields (ACF)
Due to compatibility issue with WooCommerce 3.6.x, we no longer recommend you to use these out-dated plugins, you can use ACF instead!
After installed and activated, navigate to Custom Fields menu from admin sidebar then Add New group for category, then add two fields with the same settings as in red marked area:
Scroll down and you will see the Location and Settings, these settings are crucial, it will tell ACF to create above custom fields when you edit category.
Save and now you are able to add/edit Category featured images and accent color, using data from WP Term Images and WP Term Colors.