jQuery(function ($) { 
    var visited = $('<a href="#"></a>');
    var unvisited = $('<a href="http://thisdomaindoesnotexist.squak"></a>');
    $(document.body).append(visited, unvisited);
    visitedColor = visited.css('color');
    unvisitedColor = unvisited.css('color');
    visited.remove(); unvisited.remove();
    $.extend($.expr.filters, {
        visited: function () {
            var link = $('<a>').attr('href',$(this).attr('href')).appendTo(document.body);
            link.color == visited.color;
            link.remove();
        }
    });
});