One more issue that rears it's head regarding the quest for colorimetric accuracy in the field is the multiplicity of light sources encountered. Taking a sunny day landscape or architecture shot, we have the sun and then the open sky. Just as importantly, we then have the multiplicity of environmental reflections coming in all directions. If you meter the sunlight, what happens to your accuracy as more or less of these lights mix in different parts of the scene? It's my experience that color temperature will vary over as little as a couple feet or even the angle of the metering instrument to the light sources, or the angle of the target to the main light (the sun) and the mix of other reflections, or the color of a wall or pavement or greenery and trees. It seems to me that the colorimetric accuracy would come down to only a very specific white balance in one tiny part of a scene. One would have to completely control and dominate the lighting with controlled lighting in order to have any predicted knowledge of the accuracy of a rendered color. And as Andrew has pointed out you would have to measure every color everywhere so as to have two "patches" to actually compare, an impossibility. I heartily endorse those who seek more accurate control from their equipment, but this seems to me to be a quixotic quest for anything beyond testing your individual cameras and methods to achieve a precise white balance and improved rendering engine interpretation of the camera raw data. To those in scientific or museum situations, how colorimetricly accurate would your work be if you allowed mixed color temperature lights and colored reflections over any part of the subject being photographed? I think we can agree it would be nil, as it is standard practice to eliminate those very things when doing highly accurate, measured photography. Even the subtlest variation in color temperature between two light sources used to light a target for a profile creation makes for a very bad profile. How can one possibly overcome the variations in lighting over an uncontrolled scene in order to suggest colorimteric accuracy? Spend some time doing architectural photography with existing light, limited even to exteriors so as to avoid the extra problems with fluorescents of different age and type, tungsten sources, etc., and you will well know how different color temperature varies over a scene. Scene white balance is always a compromise of individual, perceptual selection. Thanks to all. Jeff Stevensen