function onOpen() {
  DocumentApp.getUi()
      .createMenu('Utilities')
      .addItem('Auto-Replace', 'replaceSuits')
      .addToUi();
};

function replaceSuits() {
  var body = DocumentApp.getActiveDocument().getBody();
  var text = body.editAsText();


  var found = body.findText("♥");
  while (found) {
    var elem = found.getElement();
    if (found.isPartial()) {
      var start = found.getStartOffset();
      var end = found.getEndOffsetInclusive();
      elem.setBackgroundColor(start, end, "#ff0000");
    }
    else {
      elem.setBackgroundColor("#ff0000");
    }
    found = body.findText("♥", found);
  }

  found = body.findText("♦");
  while (found) {
    var elem = found.getElement();
    if (found.isPartial()) {
      var start = found.getStartOffset();
      var end = found.getEndOffsetInclusive();
      elem.setBackgroundColor(start, end, "#ffa500");
    }
    else {
      elem.setBackgroundColor("#ffa500");
    }
    found = body.findText("♦", found);
  }

  found = body.findText("♣");
  while (found) {
    var elem = found.getElement();
    if (found.isPartial()) {
      var start = found.getStartOffset();
      var end = found.getEndOffsetInclusive();
      elem.setBackgroundColor(start, end, "#008000");
    }
    else {
      elem.setBackgroundColor("#008000");
    }
    found = body.findText("♣", found);
  }

  found = body.findText("♠");
  while (found) {
    var elem = found.getElement();
    if (found.isPartial()) {
      var start = found.getStartOffset();
      var end = found.getEndOffsetInclusive();
      elem.setBackgroundColor(start, end, "#0000ff");
    }
    else {
      elem.setBackgroundColor("#0000ff");
    }
    found = body.findText("♠", found);
  }
};