I didn't get in on the original very long thread on this subject.  But I'll
add this empirical observation.
Some years back, at a body shop that did their own painting, I asked about
painting just the top of my blue/gray (almost Dove Blue but a repaint)
white of silver to minimize heating from the Sun.  It was a bright sunny
day and the shop owner led me out into the parking lot.  He led me to a
silver car parked there and told me to put my hand on it.  And the silver
car was hot, very hot.  Then we stepped over to a white car.  And it was
very cool to the touch, surprisingly so.  Question answered:  Paint the top
white.
BTW, I never did have the top painted white, came up with a reflecting
cover made from a heavy duty emergency blanket.  And that worked great for
being parked a week at a time each year in hot Sun every day.