Southcross,
paint it light - it makes a difference
did this on a an 1988 S10 - dark brown to a light tan pewter - it helped
(neither were pretty)
just changed from forest green to silver on a chrysler mini van - it helped
not arguing it was hugh difference
- obviously it does not keep people from buy black cars
there are lots of good thoughts but really bad thermo data in this thread
not going to challenge it, except to say - check this out as a data point
http://www.sae.org/altrefrigerant/presentations/sun.pdf