Google-sheets – subtract a cell value in another cell that already have one in Google Spreadsheets

Complex conditional formatting can be achieved in Google Spreadsheets using Google Apps Script. For example, you could write a function that changes the background colour of an entire row based on the value in one of its cells, something that I do not think is possible with the "Change color with rules" menu. You would probably want to set triggers for this function such as "On Edit", "On Open" and "On Form Submit".

Documentation for setBackgroundRGB() function

UPDATE: Here is a Google Apps Script example of changing the background color of an entire row based on the value in column A. If the value is positive, use green. If empty, white. Otherwise, red. See the results in this public Google Spreadsheet. (You will have to be signed in for the script to run, but without signing in you can still see results).

function colorAll() {
  var sheet = SpreadsheetApp.getActiveSheet();
  var startRow = 2;
  var endRow = sheet.getLastRow();

  for (var r = startRow; r <= endRow; r++) {
    colorRow(r);
  }
}

function colorRow(r){
  var sheet = SpreadsheetApp.getActiveSheet();
  var dataRange = sheet.getRange(r, 1, 1, 3);

  var data = dataRange.getValues();
  var row = data[0];

  if(row[0] === ""){
    dataRange.setBackgroundRGB(255, 255, 255);
  }else if(row[0] > 0){
    dataRange.setBackgroundRGB(192, 255, 192);
  }else{
    dataRange.setBackgroundRGB(255, 192, 192);
  }

  SpreadsheetApp.flush(); 
}

function onEdit(event)
{
  var r = event.source.getActiveRange().getRowIndex();
  if (r >= 2) {
    colorRow(r);
  }
}

function onOpen(){
  colorAll();
}

​

You can try adding a Google Apps Script to capture when a cell is edited and add a timestamp to a different cell. Here's a previous answer that is similar: Google Spreadsheet Timestamp?

function onEdit() {
 var s = SpreadsheetApp.getActiveSheet();
 if( s.getName() == "Sheet1" ) { //checks that we're on the correct sheet
   var r = s.getActiveCell();
   if( r.getColumn() == 13 ) { //checks the column
     var nextCell = r.offset(0, 1);
     if( nextCell.getValue() === '' ) //is empty?
       var time = new Date();
       time = Utilities.formatDate(time, "GMT", "HH:mm:ss");
       nextCell.setValue(time);
   };
 };
}