Sub sbHighlightDuplicatesInColumn()
    Dim lastRow As Long
    Dim matchFoundIndex As Long
    Dim iCntr As Long

    lastRow = Sheets("Sheet1").Range("A1").SpecialCells(xlCellTypeLastCell).Row
    For iCntr = 1 To lastRow
        If Cells(iCntr, 1) <> "" Then
            matchFoundIndex = WorksheetFunction.Match(Cells(iCntr, 1), Range(Cells(1, 1), Cells(iCntr, 1)), 0)
            If iCntr <> matchFoundIndex Then
                Sheets("Sheet1").Cells(iCntr, 1).Interior.Color = vbYellow
            End If
        End If
    Next

    'iterating over the 2 columns...

    numOfRows = ActiveWorkbook.Worksheets("Sheet1").Range("A2", Worksheets("Sheet1").Range("A2").End(xlDown)).Rows.Count
    freq = numOfRows / 12

    Dim lastRowL As Long
    lastRowL = Sheets("Sheet1").Range("L1").SpecialCells(xlCellTypeLastCell).Row

    Dim LastRowM As Long
    LastRowM = Sheets("Sheet1").Range("M1").SpecialCells(xlCellTypeLastCell).Row

    Dim rg1 As Range, rg2 As Range
    Set rg1 = ActiveWorkbook.Worksheets("Sheet1").Range("A2:A4")
    Set rg2 = ActiveWorkbook.Worksheets("Sheet1").Range("G2:G4")

    ' Create dynamic array
    Dim tmpArray1 As Variant, tempArray2 As Variant
    Dim code As Variant, value As Variant

    'Dump the range into a 2D array
    tmpArray1 = rg1.value
    tmpArray2 = rg2.value

    'Resize the 1D array
    ReDim code(1 To UBound(tmpArray1, 1))
    ReDim value(1 To UBound(tmpArray2, 1))

    'Convert 2D to 1D
    For i = 1 To UBound(code, 1)
        code(i) = tmpArray1(i, 1)
        value(i) = tmpArray2(i, 1)
    Next

    For cnt = 1 To freq
        'iterate over col-L
        Dim u As Integer, v As Integer
        u = cnt * 3 + 2
        v = u + 2

        Dim iTrack As Integer
        iTrack = 1
        'iterate over col-L
        For iCntr = u To v
            If Cells(iCntr, 8) <> "" Then
                matchFoundIndex = WorksheetFunction.Match(Cells(iCntr, 8), Range(Cells(1, 8), Cells(iCntr, 8)), 0)
                If code(iTrack) <> matchFoundIndex Then
                    Sheets("Sheet1").Cells(iCntr, 8).Interior.Color = vbYellow
                Else
                    Sheets("Sheet1").Cells(iCntr, 8).Interior.Color = vbGreen
                End If
            End If
            iTrack = iTrack + 1
        Next

        iTrack = 1
        'iterate over col-M
        For iCntr = u To v
            If Cells(iCntr, 9) <> "" Then
                matchFoundIndex = WorksheetFunction.Match(Cells(iCntr, 9), Range(Cells(1, 9), Cells(iCntr, 9)), 0)
                If value(iTrack) <> matchFoundIndex Then
                    Sheets("Sheet1").Cells(iCntr, 9).Interior.Color = vbRed
                Else
                    Sheets("Sheet1").Cells(iCntr, 9).Interior.Color = vbGreen
                End If
            End If
            iTrack = iTrack + 1
        Next
    Next

End Sub
Private Sub Worksheet_Change(ByVal Target As Range)

    Dim curColor As Variant
    curColor = ActiveCell.Interior.Color
    If Application.CountIf(Range("A:A"), Target) > 1 Then
        MsgBox "Duplicate Data", vbCritical, "Remove Data"
        Target.value = ""
        'ActiveCell.Offset(RowOffset:=-1).EntireRow.Interior.Color = curColor
    End If
End Sub

Private Sub Worksheet_SelectionChange(ByVal Target As Range)

End Sub