With all this talk of white balancing, I thought I'd share a nifty little plug-in often overlooked... the CGM's DVE vol 1, which has a plug-in for white balancing video.
So what's the difference between that and FCP's own color correction plug in? FCP's color correction tool is an awesome plug in but it is rather complicated to master and learn the ins and outs properly.
With this plug-in, you can have the choice of finetuning the RGB channels through a simple interface and also where the color correction applies to.. high, mids or low levels.

You can also choose to spot the "white" using the one touch function. It's not as accurate as the one touch on Color Correction and needs finetuning anyhow. But the interface is clean and results instantaneous.

As you can see, the results are good for a few touches of button. Obviously FCP's own Color Correction 3 way is more powerful and sophisticated. But for a free plug-in included in FCP 3, it is a very easy tool to use and the results are good.
You can upgrade to version 1.4 for $99. It's a worthwhile C-note investment.