function show(ev){
    var element = ev.target;
    element.style.backgroundColor = "white";
}

function addAll() {
    var item;
    var checks = document.getElementsByTagName("span"); 
  for (item of checks) {
    if (item.getAttribute("class") == "check") {
      item.addEventListener("click", show, false);	
    }
  }
}
window.onload = addAll;