Public ReadOnly Property SheetTabIndex As Integer

Dim instance As SheetTabClickEventArgs
Dim value As Integer
 
value = instance.SheetTabIndex

public int SheetTabIndex {get;}

private void fpSpread1_SheetTabClick(object sender, FarPoint.Win.Spread.SheetTabClickEventArgs e)
{
    fpSpread1.TabStrip[e.SheetTabIndex].BackColor = Color.Teal;
}

Private Sub FpSpread1_SheetTabClick(ByVal sender As Object, ByVal e As FarPoint.Win.Spread.SheetTabClickEventArgs) Handles
FpSpread1.SheetTabClick
    FpSpread1.TabStrip(e.SheetTabIndex).BackColor = Color.Teal
End Sub