var i = true;
function blinken() {
	if(i) {
   	document.getElementById("b1").className = "farbe2";
//   	document.getElementById("b2").className = "farbe2";
//   	document.getElementById("b3").className = "farbe2";
  }
  else {
   	document.getElementById("b1").className = "farbe1";
//   	document.getElementById("b2").className = "farbe1";
//	   	document.getElementById("b3").className = "farbe1";   	
  }
  i= !i;
}
window.onload = setInterval('blinken();', 1000);