I guess the only thing wrong in your original code was this:
Private Sub tbLinehaulPaid_Change()
Select Case cbDroppedEarly.ToString
Select Case cbDroppedEarly.Selecteditem.ToString
Case "YES" : tbLinehaulPaid.BackColor = Color.Teal
Case Else : tbLinehaulPaid.BackColor = Color.WhiteSmoke
End Select
End Sub
In order to make work the solution 2, make sure that the "YES" value is the same that the index that you have selected.
If you say that still not working... mmm... then, Make sure that you are using properly the event "cbDroppedEarly.selctedindexchanged". Take a look at the control events, maybe the link between the code and the control has broken.