Hi Joe,
The reason why white blancing on the 40D as opposed to Canon's older line up 30D,20D is from their new dual filtering layer technology. The visual wavelength is entirely different to the older types hence that is why the 40D can capture more h-alpha photons than the older types unless modifying it. Taking an object with the 40D and 20D colours will be different even with the same lense/settings etc etc. Not much but just have to put up with it or use a grey card and balance the colours in manual mode
