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It's worth noting that if you find yourself shooting under very weird lighting conditions, such as unknown fluorescents and mixed conditions, all that one needs to do is take out a ColorChecker (even the little pocket version) and take a shot of it under the unusual lighting.
Working with the color checker tab each time the light is a problem is quiet fascinating, but it doesn't work apparently. Under 4800 K, I have an error message: " Please reshoot the cast carefully to avoid color casts and try again."
And if I read the DNG editor tutorial:
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Photograph the ColorChecker Chart under a 6500 K illuminant (e.g., D65 simulator), taking care to illuminant the chart evenly and to minimize color casts.
You have to take the photograph under a 6500 K illuminant.