[Safort]

function changeDiv (id){
        if (id  == 'closedred'){
            document.getElementById('closered').style.background = 'red';
            document.getElementById('closedyellow').style.backgroundColor = 'closedyellow';
            document.getElementById('closedgreen').style.backgroundColor = 'closedgreen';
        }
        if (id == 'closedyellow'){
            document.getElementById('closedred').style.backgroundColor = 'closedred';
            document.getElementById('closedyellow').style.backgroundColor = 'yellow';
            document.getElementById('closedgreen').style.backgroundColor = 'closedgreen';
        }
        if (id == 'closedgreen'){
            document.getElementById('closered').style.backgroundColor = 'closedred';
            document.getElementById('closedyellow').style.backgroundColor = 'closedyellow';
            document.getElementById('closedgreen').style.backgroundColor = 'green';
        }
    }

А так работает?