I always look at the blue water through the viewer after every MWB. If it looks even the slightest bit purplish, do another MWB closer to the test subject or with the lights closer or brighter.
since you have mentioned it a few times, I am curious to know how you salvaged "grainy-red" footage (supposedly resulting from white balancing with insufficient red in the field of view), if you could at all...
I am using FCE, so I may not have access to all the tools you may have in FCS. But I plan to upgrade to FCPX when it comes out (after a short waiting period where I'll attentively listen to user feedback :-).
Interestingly, this happened while I was trying to MWB off my white fin decorated with a generous dose of red in the form of a couple of dive flags (precisely to follow your advice!). After MWB, I got a beautiful white and red fin image, a tad too red image otherwise (but not dramatically so, as I thought looking at my LCD screen).
I only discovered the red graininess once I downloaded my footage on my MBP. It is not dramatic, as I did not use this approach for too many shots, but in case you worked out a solution, I would definitely appreciate your advice.
PS: I will try to zoom on a red area of my fin next time I attempt this experiment. So far, I have simply framed my fin and MWB. What do you think?
As I mentioned, in other threads, I gave up on using fins for MWB. Too awkward and not reliable enough. Now I use sand, coral, rusty metal, etc. If you have framed your fin, I don't know how much the white part of the fin has effected the reading.
It is a case of practice, practice, practice; until your eye can see how the camera's sensor will react.
If you do get a mild case of the red fuzzies, in FCP, I use the 3-way color corrector, with a delimiter set for only the blue-green areas (water) and I drag the color adjuster away from red towards the blue. I play with these until I get the best balance. Depends a bit on the brightness of the water, but I find that the lighter channel needs more than the middle channel, which needs more than the darker channel. Also dropping the brightness of the lighter channel helps. A bit of playing gets it almost right. They never completely disappear but they become almost unnoticeable.
Of course, a severe case of the fuzzies is not salvageable.
If you are ever diving and are unsure if the MWB is right, press and hold and put it back to AWB then try to reduce the green in the color corrector.
PS. I suggest you copy this thread back into the forum. There is nothing private about this conversation, is there?