Hello,
There is no option in Theme Settings to change the color of the icon. You need to do it using Custom CSS.
So you need to use the menu item class to change the icon color.
For example, the bellow Custom CSS will change the color of the icon whose id will be “402”
#menu-item-402 .fa.fa-envelope-o::before {
color: green !important;
}
You can adjust the menu item class according to your needs. If you are unable then provide with the URL of the website check it myself and help you out accordingly.
Best Regards.