We have had good luck with the dark (Charcoal Tweed Sunbrella, now discontinued) curtains, particularly if we roll up the curtains and open the windows on the side opposite from the sun. That said, we try to avoid hot weather as much as possible, so IDK what they would be like in a Florida summer, for example. But I suspect they would work better than the white because they would block more radiant energy. Ask SeaWolf Joe to expound on that topic further.
Warren