I can't imagine anyone ever needing a reservation for a Shades of Green restaurant. The only time we tried was when we had a group of 18 and it was that morning and they just laughed and said to show up when we wanted and they would put together tables for us.
If you want to go to onw though you could take a SOG bus or walk from the Poly. They don't ask for ids to eat there. The ice cream place has really good prices for an afternoon snack.