After page postback, DropDownList item attributes "color" cleared ?

DropDownList1.SelectedItem.Attributes.Add("style", "Color:GREEN")
This is set when a person clicks a button, "resubmit order"... then the selected item is turned green so they know they've already fixed that order item.
Now if I select a different item, the page posts back to grab new information for another order...., but the previously set dropdownlist item, is no longer green.
I'm not refilling the dropdown, if the postback=true, so I have no idea why the viewstate is not keeping the attributes of the dropdown list items.
How can I preserve the color of dropdownlist items, after a postback ?

----------------------

Try this:

Protected Sub Page_PreRender(ByVal sender As Object, ByVal e As EventArgs)    
    For Each index As Integer In Me.SelectedItems    
        DropDownList1.Items(index).Attributes.Add("style", "Color:GREEN;background:red")    
    Next    
End Sub   
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs)    
    'DropDownList1.SelectedItem.Attributes.Add("style", "Color:GREEN");    
    Dim selecteditems As List(Of Integer) = Me.SelectedItems    
    selecteditems.Add(DropDownList1.SelectedIndex)    
    Me.SelectedItems = selecteditems    
End Sub   
Private _SelectedItems As List(Of Integer)    
Public Property SelectedItems() As List(Of Integer)    
    Get    
        If ViewState("SelectedItems") IsNot Nothing Then    
            _SelectedItems = DirectCast(ViewState("SelectedItems"), List(Of Integer))    
        Else    
            _SelectedItems = New List(Of Integer)()    
        End If    
        Return _SelectedItems    
    End Get    
    Set(ByVal value As List(Of Integer))    
        ViewState("SelectedItems") = value    
    End Set    
End Property

http://forums.asp.net/p/1159612/1913450.aspx

http://www.experts-exchange.com/Programming/Languages/.NET/ASP.NET/Q_25339597.html