Thank you for the sample. You can handle the CurrentCellShowingDropDown event and set the colors there.
Private Sub gridFavoris_CurrentCellShowingDropDown(ByVal sender As Object, ByVal e As _
GridCurrentCellShowingDropDownEventArgs) Handles gridFavoris.CurrentCellShowingDropDown
If TypeOf (Me.gridFavoris.CurrentCell.Renderer) Is GridDropDownGridListControlCellRenderer Then
Dim cr As GridDropDownGridListControlCellRenderer = Me.gridFavoris.CurrentCell.Renderer
cr.ListControlPart.Grid.TableStyle.BackColor = Color.White
cr.ListControlPart.Grid.Properties.BackgroundColor = Color.White
End If
End Sub