I figured it out:
Add the following code to your custom.css:
#top .main_menu .menu .custom-menu-item a { color:red; }
#top .main_menu .menu .custom-menu-item a:hover { color: green; }
Then go to WP Appearance/Menus and set “custom-menu-item” class in the “CSS Classes (optional)” of your menu item.
If you can’t find “CSS Classes (optional)”, then please watch this quick video: http://www.youtube.com/watch?v=5Uncd4pjTuE
Thanks)