Originally Posted By: wfaulk
Regardless, there is a (vague) point at which the light provided by the sun starts to change in color temperature (which I assume to be at or near the time that the sun appears to start descending below the horizon)

Actually I suppose what you're really talking about here is sunset redness, which depends on the length of the in-air path of the sunlight, so it actually starts increasing very slowly as soon as the sun leaves the zenith, and might already be changing significantly before the sun's disk hits the horizon.

Peter