Hello
To color the icon for a particular menu item you can add the following to the Custom CSS field of your templates parameters where 541 is your menu item ID (edit to match)...
#hornav .menu li.item-541 [class^="fa-"]::before,
#hornav .menu li.item-541 [class*=" fa-"]::before {
color: #516688;
}
CiarĂ¡n