My problem is not the white balance but the lack of light. It takes very good light to get a good red, then, as you say, you can ajust the intensity of the light in photoshop or a similar program to get more details, something you can't do very well if the light is insufficient to begin with. Now that I have much brighter lights available, I find it a lot more easier to get more accurate colours. But I'll read the guide again, I always find something new when I read it.
True, when the light is very low.When there is no enough light it is difficult for the camera to adjust itself to the color of the light.
To simplify this a bit:"Why do bright red flowers overexpose?"
http://forums.dpreview.com/forums/readflat.asp?forum=1036&message=38349987&changemode=1
The gray card doesn't really have anything to do with rendering color, as such.
What happens if you use a gray card under florescent lights, without fixing the white balance for that light source. Will you get accurate color?
One of your sources clearly states: "The grey card is put into the image so that the light falling on the subject also falls on the grey card. The white balance reading is taken from the card..."
Certainly there is a big difference between what I term as "taking" a picture (camera) and "making" a picture (computer). Certainly using a neutral gray in Photoshop RAW or jpeg using the RAW setting in Photoshop will help with color correction after the photo has been made by the camera.
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