I use the following sub to set item styles.

   Private Sub SetArtistStyle()
       Dim i As Integer = 1
       For i = 0 To ListOfArtists.Items.Count - 1
           Dim li As ListItem = ListOfArtists.Items(i)
           Select Case i Mod 2
               Case 0
                   li.Attributes.Add("style",
"background-color:SkyBlue;color:Black")
               Case 1
                   li.Attributes.Add("style",
"background-color:Silver;color:Black")
           End Select
       Next
   End Sub

The code is executed after a DataBind on the dropdown.  If you are not using
databinding then you can use this a version of the code in the above routine
after you create the dropdown item.

Hope this helps
Lloyd Sheen