I don't think there would be a lot of difference between the two. The tinted windows provide a lot of shading, the only large heat sink is that dashboard - one of Tim's sunscreens could take care of that.
The black exterior would soak up a lot of heat, but over most of the car there's an air space between the interior and exterior, so there's not a lot of conductive heat transfer.
On top of all that, the X's air conditioner has more cooling power than most homes! Not to worry.
I live in Miami, and these were the two color combinations I was choosing from. I actually asked the dealer, and he feels there is no noticable difference between them. It stands to reason that black exterior would be the hottest, yet I own currently a Black Legend with saddle interior, and it rarely seems hot.