Submenu colors are a bit tricky to change, but with a little bit of patience, you can easily change their color. By the time of writing this article, there were no plugins available for changing the color of submenus, but maybe in the future, there might be such plugins.
Currently, there are two methods by which a person can change the color of the submenu in WordPress:
- By using the customize option.
- By using CSS.
For further detail you can search How to change background color of submenu in Wordpress