Sub Demo()
Application.ScreenUpdating = False
Dim lRow As Long, lCol As Long, r As Long, c As Long
With ActiveSheet
  .UsedRange
  With .Cells.SpecialCells(xlCellTypeLastCell)
    lRow = .Row
    lCol = .Column
  End With
  For r = 1 To lRow
    For c = 2 To lCol
      If Application.WorksheetFunction.CountIf(.Range(.Cells(r, 1), .Cells(r, c)), .Cells(r, c).Value) > 1 Then
        .Cells(r, c).Font.ColorIndex = 3
      End If
    Next
  Next
End With
Application.ScreenUpdating = True
End Sub