function cellOver(tableCell, imageId){
	imagesrc = document.getElementById(imageId).src;
	imagesrc = imagesrc.replace('green','yellow');
	document.getElementById(imageId).src = imagesrc;
	tableCell.className='nav_active';
}

function cellOut(tableCell, imageId){
	imagesrc = document.getElementById(imageId).src;
	imagesrc = imagesrc.replace('yellow','green');
	document.getElementById(imageId).src = imagesrc;
	tableCell.className='nav_inactive';
}