function colorAlternatingRows ()
{
  allRows=document.getElementsByTagName("tr");
    for (i=0; i < allRows.length; i++)
    {
        if (i % 2 == 0) // if the row is odd
        { 
        $(allRows[i]).css("background-image","url('../images/gray50.png')"); // give it a gray background
        }
    }
}

$(document).ready(function(){
    colorAlternatingRows ();
});