OK
1. Dashboard > Appearance > Menus
Click Screen Options top right of window. Check the CSS Classes. Close the options.
2. Edit the menu, select the item you want to change color.
In the CSS Classes field add: custom-color
3. Customizer > Additional CSS add this code and change the hex codes for your colors.
.main-navigation .main-nav ul li.custom-color a {
background-color: #ffffff;
color: #000000;
}
4. To add a hover color add this additional code and again change the hex codes:
.main-navigation .main-nav ul li.custom-color:hover a {
background-color: #ffffff;
color: #000000;
}