Have a try my macros. You can possibly modify them according to your needs.
Macro to be pasted in the sheet's module, it will highlight cells in column C if changed:
Code:
Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
If Not Intersect(Target, Range("C2:C" & Cells(Rows.Count, "C").End(xlUp).Row)) Is Nothing Then Target.Interior.ColorIndex = 6
End Sub
Macro to paste into the ThisWorkBook module, when the file is opened for the first time in the day it will remove highlighting in column C cells if today's date is later than the last day the file was updated (saved):
Code:
Option Explicit
Private Sub Workbook_Open()
If WorksheetFunction.EDate(CreateObject("Scripting.FileSystemObject").GetFile(ActiveWorkbook.Name).DateLastModified, 0) < WorksheetFunction.EDate(Now, 0) Then Range("C2:C" & Cells(Rows.Count, "C").End(xlUp).Row).Interior.ColorIndex = xlNone
End Sub