MHD: Not really how it mixes colours, but how it maps the raw sensor data into a curve representing the light levels.
I've extensively experimented with fotogenic's curves, as well as alfonso's. I forgot the link to alfonso, but google might be helpful (and fotogenic is synonymous with custom curves, you should have no trouble finding it).
Basically, the white wedding curves at any version attempts to correct the perceived underexposure of the standard tone curve. It only
modifies slightly the highlights to extend dynamic range. For me, I'd rather save the custom curve spot in camera for something else and just dial in positive exposure comp when I want the 'white wedding' effect (keeping a close eye on blown highlights).
Alfonso's curve also corrects the perceived underexposure at midtones, but it abruptly cuts off the high end (shapes all values beyond 220ish to 220 IIRC, out of the 255 light levels). Which prevents blown highlights completely, but at the cost of dynamic range and ultimately overall scene contrast (even setting +3EV and shooting a white wall will render a histogram curve contained within the right hand edge). I really like the results of this curve, except from a technical point of view cutting off values beyond a certain point is not ideal in terms of optimising image parameters (i'm a technical man first, artistic/creative man nth)... reasoning came from Michael Reichman's article Expose to the Right, suggesting that half of an image's data is contained within the first stop of light levels, hence cutting these values off would imply losing alot of potentially good data. This is still a purely academic arguement, and photography being an artistic/creative endeavor, I'm sure it does not impact the perception of an image as greatly as the academic arguement makes it out to be....
Anyway, I've stuck with using fotogenic's Provia v3.4 - because I initially liked the results (paired with enhanced saturation setting), and because I'm too lazy to experiment some more. My camera settings experimental stage has long gone (it's been 6 months since I got my D70), and now I try to learn and adapt to the camera settings chosen (which I considered ideal at the time of choosing them).