The MDX is cool
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.
But JTM's right, silver is THE color!