White balance is a much more complicated topic then it seems on the surface. The deeper you go, the more confused it is possible to get.
One of the things I try to keep in mind with white balance is that the raw image converter needs a neutral reference in order to eliminate color casts in your photograph due to the temperature of the illuminant light. I don't think it matters whether you use a white object, a light gray object, or the Digital Grey kard (http://hTtp://www.digitalimageflow.com
) which my company makes. (but see below)
It is interesting that Photoshop Lightroom allows the user to adjust the color temperature into a JPEG file. I actually don't understand exactly how this is accomplished in the software and I need to find out more. Perhaps one of the users of this forum can comment on this interesting feature of Lightroom.
The really important feature is that the object you do use spectrally neutral. A truly neutral white balance reference, or gray card, acts as a color temperature mirror, and it faithfully reflects the true nature of the light that falls on it back into the camera's digital sensor, without adding, subtracting, or altering the light in any way.
It's helpful to use a gray surface rather than a white surface, because the white surface can be blown out, which in technical terms means that the image sensor will have exceeded its maximum brightness value in that particular area. A gray card will not blow out.
In achieving white balance, what we are achieving its color constancy. This is a way of saying that the color of objects appear the way we expect them to appear across a wide range of illuminant light sources. Human eye and brain is used to seeing objects remain constant in color, and we perform a mental white balancing on things we see in order to maintain color constancy of objects in our environment.
When lit by light of varying color temperature, the light reflected off an object will actually be quite different and it normally would appear different to our eyes, just as it should. However, the brain performs a sophisticated type of white balancing in order to maintain color constancy. This makes it easier to recognize familiar objects in our environment. Imagine if you went to look for your car in the parking lot and the color was radically different in every garage depending on the light! I suspect you'd end up walking home a lot! This is why color constancy is important to the human brain, and why color constancy is important in digital photographs.
I recommend my white balance product - the Digital Grey Kard - as a simple, economical, and highly accurate solution for your white balance problems.