is the hood of a black car really hotter in the sun than a white one?

Hello Harmaster1,

The short answer is yes.

There are a number of sites that explain the temperature difference of
light (or white) colored items and dark (or black) colored items. For
example
  http://www.mansfieldct.org/schools/mms/staff/hand/convcondrad.htm
has an explanation of a radiograph at the bottom of the page. The
radiograph spins in one direction when lit up because the air on the
black side is more energenic than the white side. If you remove the
light and wait long enough, you may also see the radiograph spin the
other way when the black side cools off faster than the white side.

Another example is at
  http://www.faqs.org/faqs/bicycles-faq/part4/section-25.html
which describes a test done on bicycle helmets, even with a "wind"
blowing across the helmet, there was a measurable difference between
the black and white helmets.

The last way to determine the exact amount of the difference is to
measure the temperatures as in the above example using a pair of cars
(black and white) and a temperature sensor (even a thermometer) to
measure the difference.

Some good search phrases include
  black white surface temperature difference
  radiograph black white
and similar phrases.

If you need further specifics, please make a clarification request.

  --Maniac

In general, black colored materials will reach higher maximum
temperature due to visible frequencies of solar radiation than those
colored white. The white is that color because it's reflecting rather
than absorbing. (At least it is in the visible band.) Look at
spacesuit designs. They're typically a very clean, bright white color,
and the reason is to reflect as much sunlight as possible. A silver
mirrored surface is even better. The Apollo command module had a layer
of highly silvered mylar taped to it snugly. When Apollo 13 had to
shut down the heater to conserve power, the inside temperature
actually got uncomfortably chilly, despite the very high temperature
of the incident sunlight. It's not practical, however, to always
silver surfaces such as on spacecsuits, so the next best thing is pure
white.

   Another issue, however, is how absorptive a material is in the
infrared. If it's selectively absorptive in IR, then it's quite
possible for it to attain a higher temperature even if it's highly
reflective in the visible frequencies.

-Mark Martin

Titanuim Dioxide is used im many White paints because it reflects
almost all light in the visible spectrum, and in many sunscreens
because it also reflects UV light.  light is made up of many small
packets of energy, and an absorbent (black) surface will change that
light energy into heat (kinetic) energy.  a perfectly white surface
(entire EM spectrum) will not get hot in sunlight

An interesting related side light is that the bottom of the spacecraft
is also black...this is because of the duality of nature ie if
something is the best absorber is is also the best radiatior and this
is used all over the place the under side of the space craft to
radiate off the energy encountered when reentering the atmosphere as
well as the back side of "older" fridges to radiated the heat from
compression before it returns inside...this idea of duality in nature
is all over the place and is a neat topic to think about...what if
there was no duality?...

just something to think about,
kmc