Sub HighLightCells()
ActiveSheet.UsedRange.Cells.FormatConditions.Delete
ActiveSheet.UsedRange.Cells.FormatConditions.Add Type:=xlCellValue, Operator:=xlEqual, _
    Formula1:=ActiveCell
ActiveSheet.UsedRange.Cells.FormatConditions(1).Interior.ColorIndex = 4
End Sub

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
 call HighLightCells
End Sub

Sub HighlightCells()
Dim rCell As Range

If ActiveCell.Value = vbNullString Then Exit Sub

Set rCell = ActiveCell

Do
    Set rCell = ActiveSheet.UsedRange.Cells.Find(ActiveCell.Value, rCell)

    If rCell.Address <> ActiveCell.Address Then
        rCell.Interior.Color = 65535
    Else
        Exit Do
    End If
Loop

End Sub