This is how you add a class to menu items in WordPress. Change the "theme_location" to == "primary" to any menu name you like. Or remove the condition to have it applied everywhere.

add_class_to_menu_items

add_filter( 'wp_nav_menu_objects', 'add_menu_class', 10, 2 );
function add_menu_class( $sorted_menu_items, $args ) {
  if ($args->theme_location == "primary")
		foreach ($sorted_menu_items as $i => $menu )
			$sorted_menu_items[$i]->classes[] = 'color-'.strtolower(str_replace(' ', '-', $menu->post_title));

	return $sorted_menu_items;
}