function setBackgroundGrille() {
var td, ntd
var trs = document.getElementById('grille').getElementsByTagName('tr');
for (var i=0; i<trs.length; i++) {
tds = trs[i].getElementsByTagName('td');
for (ntd=1; ntd<tds.length; ntd++) {
tds[ntd].style.backgroundColor = (ntd%2 ? '#CFF' : '');
}
}
}