var result = 0;
var myEvent = function() {
  if (result == 0) {
    document.getElementById('my-button').style.backgroundColor = '#4cff00';
    result = 1;
  } else {
    document.getElementById('my-button').style.backgroundColor = '#6b7077';
    result = 0;
  }
{
    var xmlhttp;
    if (window.XMLHttpRequest)
{
    xmlhttp = new XMLHttpRequest();
    var n_JSON = JSON.parse(xmlhttp.responseText);
    var ID = n_JSON.ID;
    var result = n_JSON.result1;
}
    if (ID == 1 && result == 0)
{
  var xhr = new XMLHttpRequest();
  xhr.open('POST', "con_data_ajax/work-ajax-data.php?user-work="+user+,true);
  let body = 'result=' + result;
  xhr.send(body);
  if (xhr.status == 200) {
    document.getElementById('result').innerHTML = result;
  }
}
#my-button {
  background-color: #6b7077;
}
<button id="my-button" onclick="myEvent()">в работе</button>
<div id="result">0</div>

$answer = '{"ID":"0", "Name":"xxx"}';

if(($_POST['login']=="tech_user") AND ($_POST['pass']=="111")){

    $answer = '{"ID":"1", "Name":"Копыча"}';

}
if (($_POST['ID']=="1")) {
$answer = '{"result":"1"}' ;
OR
$answer = '{"result":"0"}' ;
}