The mouse over doesn't make a selection, so I believe the answer is no.
However, if you want the controltiptext to change when the user makes a
selection then in the afterupdate event use a select case routine to change
the controltip based on user selection:
Private Sub Combo0_AfterUpdate()
Select Case Combo0
Case "Red"
Me.Combo0.ControlTipText = "This is red"
Case "White"
Me.Combo0.ControlTipText = "This is White"
Case "Blue"
Me.Combo0.ControlTipText = "This is Blue"
Case "Yellow"
Me.Combo0.ControlTipText = "This is Yellow"
End Select
End Sub