[Jeph]

COLORS
Darker = hotter
On a hot day, put the back of your hand on a white car, then try a dark car. Same goes for the interior. IF this concerns you, go light-colored. Conduct some research, go to the dealer on a hot day and feel the colors you like.

TINT
Go to a tint specialist. I was worried about some inexperienced kid puting on my tint at first. But if you think about it, IT'S JUST GLASS! Hyundai or Ferrari, it's just glass. They're cheaper and sometimes they'll let you go darker than what's typically allowed (to save you a few degrees inside the car). The only thing that bugs me is a non-tinted rear window, which you can't do if the back window is plastic. Furthermore, dealers usually just send it to the specialist anyway and add a heft markup. Ask around in your area from people with tinted windows.

AC
My Boxster's AC is fantastic (and I'm here in TEXAS).

LOCAL DEALERS
I like the Seal Gray on gray/gray. First off, it just sounds cool. It's dark LIKE black (if you like black, it's a great alternative). I stray from black because keeping it clean can be rough. I don't know if it'd be the coolest. Perhaps the silver gets the "cool" award. The black and blue Boxsters will be hotter (thermally speaking).