Issue on Setting $icon_url Parameter on WP add_menu_page()

The link you provided has the answer, given by Otto as a comment:

Short answer is that you can’t. Not only using add_menu_page like
that. Those icons WordPress uses are added as background images via
CSS, not using the icon_url method that is provided with
add_menu_page.

As you said the syntax is:

syntax: add_menu_page( $page_title*, $menu_title*, $capability*, $menu_slug*, $function, $icon_url, $position ); – * required

So I used my custom icon (home.png), placed in a folder (/my_theme/admin/images/) as:

add_menu_page(  
    'Site Options',                     // The title to be displayed on the corresponding page for this menu  
    'Site Options',                     // The text to be displayed for this actual menu item  
    'manage_options',                   // Which type of users can see this menu  
    'sandbox',                          // The unique ID - that is, the slug - for this menu item  
    'sandbox_menu_page_display',    // The name of the function to call when rendering the menu for this page
    get_bloginfo( template_directory ) . '/admin/images/home.png'   // Icon for the Main menu in Admin panel
);