modify nav menu args

//Add jetmenu blue class to the megamenu plugin

function modify_nav_menu_args( $args )
{
    if( 'primary' == $args['theme_location'] )
    {
        $args['menu_class'] = 'jetmenu blue';
    }

    return $args;
}

add_filter( 'wp_nav_menu_args', 'modify_nav_menu_args', 20000 );