Simon, I've been following this string with interest, I also just got the FS100 and am having WB issues as well.
I was just at the Galapagos and didn't have much luck with MWB, it seemed to add to much red. The water wasn't the nice blue that you get at Socorro but more green to brownish at the thermocline.
I see all of your test pics. and am wondering what you were using for your WB card? White? Gray? The Sun? The Amphibico slate if so which side? Sand?
It made a big difference with my old Z1.
Are you getting the saturated green colour issues like others have posted in this thread? The water at San Benedicto was certainly a little green, but I didn't get those issues unless I was using the preset K temperature settings.
I mainly used the palm of my hand to WB, but I did occasionally use the sun/water surface and sand when there was some around as I found that I sometimes needed to try different methods to get the best result.
In general I found that it wasn't good to push the WB too much. By that I mean if I had a good WB on WB-A at say 15m there was no point loosing that by trying to WB at 25m. Instead I'd try to WB at 25m on WB-B and if it didn't work I'd just revert back to WB-A. I found getting good results on WB below 15m to be problematic. There is a certain knack to looking at a viewfinder/lcd screen/monitor underwater and knowing if the WB is working or not. What I found with the FS100 was that if it looked too red underwater then it would almost certainly look bad once I reviewed the footage.
I also should add that the flatter the Picture Profile the better. I ended up shooting with the PP OFF, but I tried out most of them. PP1 and PP2 worked ok, but by the time you get up to PP5 (which I normally use topside) and PP6 it wasn't looking great at all. I also tried G-LOG and it worked ok, but not enough of a difference maybe to warrant the extra colour correction in post especially as there could be issues working with the footage.
I guess I'd sumarise this camera as good at the surface and good for using with lights. I think there is a strong chance that for the ambient available light shooting that I normally prefer that I'll never be fully satisfied with the results.
Edited by SimonSpear, 05 February 2013 - 06:13 AM.