It doesn't matter. They'll all get heated to the same temperature (+/- a few deg) given enough time. Maybe the black will get heated up faster.
Mythbuster had an episode on it. Don't remember the results.
uv blocking, ir blocking, solar blocking, privacy glass--can someone explain the differences please?
it does seem that heat blocking and uv blocking are directly related to the darkness of the glass.
The JX has UV blocking (reducing?) glass all around. I've sat in two JX's side by side in a parking lot with wheat and graphite interior. No really noticeable difference in inside car temp. Both were better than my Pilot with gray seats and a nearby MDX with black seats. I can only ascribe this difference to the UV glass. The other real benefit of the UV glass is that over time, the interior should hold up better than comparable vehicles w/out the UV glass.
Bottom line: get the wheat interior if you like the color and don't have little kids. Get the graphite interior if you have rugrats putting all sorts of crap on your seats all the time.