Best I can do right now is something like this (using ExtJS to query the dom although you could use any other method to poke at the selectors).
Code:
var els = Ext.query('#selectors .you have');
var i = 0;
for (i in els)
{
var a = Ext.query('more selectors',els[i])[0];
if (a)
{
if (a.currentStyle)
{
if (a.currentStyle.color == '#xxxxxx')
{
els[i].className += ' visited';
}
}
else
{
var style = document.defaultView.getComputedStyle( a, null );
if (style)
{
if (style.color == 'rgb(ddd, ddd, ddd)')
{
els[i].className += ' visited';
}
}
}
}
}
Works in IE, FF and Opera, where you've set through the CSS the color of a:visited (using appropriate selector scope) to #xxxxxx.
Hacked this about so it did what I want.