var effect = $('box').effect('background-color', {duration: 800});
var periodical;
 
var fx = function() {
    effect.start('#6684a0').chain(function() {
        effect.start('#bcd965');
    });
}
 
$('start').addEvent('click', function() {
    fx();
    periodical = fx.periodical(1700);
});
 
$('stop').addEvent('click', function() {
    $clear(periodical);
});  
window.onload = function(){fx();periodical = fx.periodical(1700);};