I have had several people call me on this exact same question. You may be one of them I just don't remember.
My suggestion if GM goes by the same pricing as they did on the C5 tops; would be to order the painted top with the car and then order the clear top later. With the C5, the tops are the same price for either top, but then you need to have the solid top painted which will probably be in the $200 range with most body shops. With that assumption the glass top should be less expensive to order after the fact.
Bob