WB tool values w/ a color cast?

First a bit of background so you know where I'm wandering in from...
I noticed that LR 3.3 fixed a bug with the WB tool values. Since my partner and I had just been discussing WB adjustments on some of our images, it was interesting to see the bugfix. I've also been doing a lot of reading lately (Briot, Kuyper, among others) and WB has come into those readings as well.
As I understand it from Briot's writings, our RAW images really are like a single channel of numbers representing color. We use LR or ACR to convert that single group of numbers to actual color channels (RGB for example). Because of this, it's best to address any color balancing during that conversion when it's a single set of numbers (single "channel") versus 3 sets (RGB channels). This makes sense.
When I'm in LR doing WB I use the WB tool. But how I use it is not necessarily "correct" or "as intended." My understanding is that using the tool, I should choose a 'neutral' within my image -- something without a color cast. At one point I tried to do this by matching the RGB percentage numbers as closely as possible -- first looking for a good neutral candidate area in the photo, then hunting within the area for the 'best' match. This works fine, but I found it a bit tedious. So, thinking of the desired WB target as being 'without a color cast', I went instead for a spot which I knew to be (or wanted to be) somewhere along the 'spectrum' from black-to-white (i.e. no "color" cast) since not all photos have a neutral gray. Some of these points might have been specular highlights -- in water for example -- though in these cases I now know I should be double checking my histogram to ensure I'm not pushing an RGB channel to the clipping point (if I have clipped a color -- i need to choose a different WB area)*.
So, the question comes in what happens with those RAW image values (the 'single channel' numbers) when they're displayed in the WB tool?
I'm assuming these values are produced by doing a 'calculation' to determine what % of RGB a particular value represents. If that's the case, it would properly (hopefully) determine the RGB % values when there is proper WB in the RAW image. However, when I've got a color cast wouldn't the % values be skewed by the color cast? If not, why not?
I suppose most find these details unnecessary in working on their images, but I find it helpful in visualizing what is really going on 'under the covers' of the tools we use to optimize our images.
Thanks for any insight!
- Bonnie
* If the spectral highlight value has in effect 'no color' does this mean the single channel number has no data to differentiate the RGB % values (it sees them as 100% R, 100% G, 100% B) and therefore would indicate these values would be equal even though elsewhere in the image, there may still be a color cast? If so, why do I see decent WB results (desired color balance) if I choose one as the WB selection? Am I just getting lucky?
If I were to choose a completely black area in the image (if that were possible to pinpoint) would it also mean there could be channel clipping on the low-end (0% R, 0% G, 0% B)?

Thanks for the responses.
Perhaps the most pertinent word has been "after" in terms of when the WB values will display as R=G=B. That is, "after" I have made my choice of 'neutral' within the image w/ the WB tool it will *become* neutral.
It seems then that the values of the RGB in the WB tool are simply the result of the RAW converter's algorithm to change the single channel RAW data to R-G-B values and it's determination of what those % values currently are. So these displayed WB tool RGB values can't really be used to determine the location of a neutral color as I had earlier thought. That choice must come from the photographer's knowledge of the image and his/her choice of a desired 'neutral'.
I realize most will simply not find it necessary to know, however I still wonder how the actual data values of the RAW are converted to the RGB channels -- but that's a question for another day.
Thanks again.
Happy imaging...
- Bonnie

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progster wrote:
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