I live in FL and have two cars with black interior. My third car is tan interior. I even owned two Touaregs previously, one with tan, one with black interior. I'm not convinced that black interiors are a lot hotter than tans - if the car's been out in the sun, it's fucking hot no matter what color it is.
Someone ought to do an experiment to actually test this theory - I'd think it's pretty simple to set up. Identical cars except for interior, park them next to each other, put thermometers in the same place in both.
Tan (or sand or beige) is hard to keep pristine - the parts where you touch it get darker over time (that's dirt, not patina
) even if you are careful and never stain it. Even if you think yours is nice looking, have it professionally detailed and you'll be surprised at the difference