Public ReadOnly Property ColumnViewportIndex As Integer

Dim instance As LeftChangeEventArgs
Dim value As Integer
 
value = instance.ColumnViewportIndex

public int ColumnViewportIndex {get;}

private void fpSpread1_LeftChange(object sender, FarPoint.Win.Spread.LeftChangeEventArgs e)
{
if(e.ColumnViewportIndex == 1 && e.OldLeft == 0)
{
fpSpread1.ActiveSheet.Columns[e.NewLeft].BackColor = Color.Yellow;
}
}

Private Sub FpSpread1_LeftChange(ByVal sender As Object, ByVal e As FarPoint.Win.Spread.LeftChangeEventArgs) Handles FpSpread1.LeftChange
If e.ColumnViewportIndex = 1 And e.OldLeft = 0 Then
FpSpread1.ActiveSheet.Columns(e.NewLeft).BackColor = Color.Yellow
End If
End Sub