Set cell background of cell after value is appended

I have a script that is appending the value in cell D2 then adding one to that cell, basically stacking a list of numbers. To make it more user friendly, I want to activate the latest cell (which works), but I also want to set the background color to cyan for 2 seconds so the user knows exactly where to go.

I have it close, but instead of seeing the cyan color, I'm just seeing the row activate.

Any thoughts?

function copynewentry() {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var idstoadd = ss.getSheetByName("Resources");
var fulllist = ss.getSheetByName("Daily");
var tag = idstoadd.getRange('D2');
Logger.log("Option#1 - Start")
// step 1 - get the last row on the target: Full List
var last_row = fulllist.getRange(1, 1, fulllist.getLastRow(), 1).getValues().filter(String).length;
Logger.log("Step#1 - the last row on fulllist = "+last_row)
// step 2 - create a target range (or at least the top left corner of the target)
var targetrange = fulllist.getRange(last_row+1,1);
Logger.log("Step#2 - the target range will be "+targetrange.getA1Notation())
// step 3 - create a source range
// how many header rows
var numheaderrows = 0
// so the range will be...
// var sourcerange = idstoadd.getRange(1+numheaderrows, 1, idstoadd.getLastRow()-numheaderrows, 1);
var sourcerange = idstoadd.getRange('D2');
Logger.log("Stewp#3 - the sourcerange = "+sourcerange.getA1Notation());
// step4 - copy from source to target
// method = range.copyto
// so copyto from the source range to the target range
sourcerange.copyTo(targetrange,{contentsOnly:true});
Logger.log("Step#4 - copied the source range to the target range and flushed");
tag.setValue(tag.getValue() + 1);
lastRowOfCol(1); //Enter the column number you want to use as the base of the search
// step 6 - apply all the pending changes.
SpreadsheetApp.flush();
Logger.log("Step#6 - Flushed the spreadsheet")
Logger.log("Option#1 - Completed")
return false;
}
function lastRowOfCol(column) {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var sheet = ss.getActiveSheet();
var total = sheet.getMaxRows();
var values = sheet.getRange(1, column, total).getValues();
for (var i = total - 1; values[i] == "" && i > 0; i--) {}
var last = sheet.getRange(i + 1, column);
var range = sheet.getRange(i + 1, 1, 1, sheet.getLastColumn());
sheet.setActiveRange(range);
const bgColor = last.getBackground();
last.setBackground('cyan');
Utilities.sleep(2000);
last.setBackground(bgColor);
}

In your script, how about the following modification?

From:

last.setBackground('cyan');
Utilities.sleep(2000);

To:

last.setBackground('cyan');
SpreadsheetApp.flush(); // Added
Utilities.sleep(2000);

Added:

About the following additional question,

> should I be adding multiple spreadsheetapp.flush's throughout my code? i thought just having one at the end sets the code to do every action and not proceed unless the action above is completed. is that not correct?

I think that it is No.

For example, when you want to show the current situation during the script is running, it is required to use SpreadsheetApp.flush(). When your script is used as a test when the following modification is used,

last.setBackground('cyan');
SpreadsheetApp.flush(); // Added
Utilities.sleep(2000);
last.setBackground('red');
Utilities.sleep(2000);
last.setBackground(bgColor);

the red color cell cannot be seen. On the other hand, when the following modification is used,

last.setBackground('cyan');
SpreadsheetApp.flush(); // Added
Utilities.sleep(2000);
last.setBackground('red');
SpreadsheetApp.flush(); // Added
Utilities.sleep(2000);
last.setBackground(bgColor);

the red color cell can be seen.