> a California beekeeper remarked that the bees prefer black plastic foundation and, to my surprise I found that seemed to be true.  

We say something is "Black" because we experience of the absence of reflected color.
A "Colored" surface is one that scatters some visible light in certain frequencies so our eyes register it as "having a color".
A "White" surface scatters/reflects light in a wide range of (or "all") color frequencies.

Anything not reflected/scattered is absorbed, so yes a "Black" object exposed to the same heat as a "White" object will be measurably warmer, every time.

The bees are heating up the foundation as a part of the comb drawing process, so the black will be "easier to warm up" than the white, all things being equal, but a far more important factor is the thickness of the plastic. 

The difference should be "black and white" if measured with thermocouples on the surface of the plastic foundation, but one would need tiny little heat shields over each thermocouple to get it to only read the plastic temperature, not the radiated heat.  I'm going to guess that the beekeepers that noticed a difference were seeing combs drawn out in hot weather/climate.  

I found the much thinner white foundation to be consistently drawn out more quickly than the thicker black foundation.  I forget which is which, but there is a plastic foundation out there that is about half the weight/thickness of the usual, and thinner (less mass per sq inch) means that the bees can heat up a small area more easily.   So, in hot weather in spring, yes black foundation will be warmer before the bees start to heat it up, and will retain more "bee radiated heat", but I'd still go with the thinnest plastic I could find.

This absorbing and reflecting of radiated heat will work the same, even in total darkness, of course.
So, paint the inner surfaces of your solar wax melter black for a performance increase, and avoid dark upholstery for convertibles.
Some snakes can detect heat (and thereby locate prey) with their "pit organs".

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