Not sure if the OP is still researching, but here is a link to a discussion over on Wetpixel about manual white balance. Pretty good info with pictures showing the differences between AWB, MWB and different MWB references.
Manual WB, is it really necessary? - Wetpixel :: Underwater Photography Forums
Biggest decision on MWB is not if it makes a difference. It's if you are willing to pay for the housing/camcorder that let you easily access it underwater.
Manual WB, is it really necessary? - Wetpixel :: Underwater Photography Forums
Biggest decision on MWB is not if it makes a difference. It's if you are willing to pay for the housing/camcorder that let you easily access it underwater.