> I'm pretty sure somehow that the /spectrum/ of the whitepoint should 
> matter for such things as dispersion, but where and why adaption come into 
> play still eludes me.

They were talking about (which I didn't get initially) how to make a certain 
*surface* look correct on a monitor, not a particular spectrum/colour.

Obviously the colour a surface appears to your eye depends on what colour 
light you use to illuminate it with.  Adaption comes into play when someone 
else has measured the "apparent" surface colour using one type of 
illuminant, but you want to know what colour it will look when lit with 
another illuminant.  If you know the viewing conditions under which you are 
looking at your monitor (eg D50 illuminant) then you can work out what to 
display on your monitor to make it look identical to if you had the actual 
surface next to your monitor.

> So the starting point is the /tristimulus/, which (basically) models how 
> strongly the three different color receptors ("cones") in the human eye 
> react to different wavelengths.

Tristimulus values can be any 3 parameters that you decide to use, a bit 
like how you can use (almost) any set of 3 vectors to describe all points in 
3D space.  The most common used are XYZ, and they don't really match with 
the cone response curves, they're just 3 parameters.

> Experiments were conducted to measure this per-wavelength response (a bit 
> indirectly) in a manner that, to my understanding, only yielded /relative/ 
> results:

No, I think they were able to generate pretty accurate colour matching 
functions, which mapped exactly how the intensity of each wavelength 
corresponded to the tristimulus values.  You end up with a chart like the 
one on wikipedia:

http://en.wikipedia.org/wiki/File:CIE_1931_XYZ_Color_Matching_Functions.svg

> Thus, the immediate conclusions drawn from these experiments left open the 
> question what "white" is

The only universal "scientific" definition of "white" I can think of is 
equal energy at all wavelengths, this gives XYZ=(1,1,1).  Other whites are 
usually related to the colour of a hot object, eg D65 is the colour of an 
object at 6500K.

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