var abg = 0;
var abgcol = "#705C5C";

function bgchange(newbg)
{
var aktiv = "../../pic/dunkel.jpg";      //Lila dunkel
var inaktiv = "../../pic/hell.jpg";    //Lila hell

document.getElementsByTagName('td')[abg].background = inaktiv;
switch (newbg) {
    case 0: document.getElementsByTagName('td')[0].background = aktiv;
    break;
    case 1: document.getElementsByTagName('td')[1].background = aktiv;
    break;
    case 2: document.getElementsByTagName('td')[2].background = aktiv;
    break;
    case 3: document.getElementsByTagName('td')[3].background = aktiv;
    break;
    }

abg = newbg; //actual background = new background
}