I do a lot of scubadiving and take my SX230 running CHDK with me, allowing me to shoot in RAW. The RAW format definitely allows me to post-process the images properly and adjust the whitebalance where needed.
However...when diving, the light changes every few meters while de- or ascending; when shooting in a cave; when a cloud blocks direct sun; etc.... Basically, you should be adjusting your whitebalance every few minutes - which I do, despite the RAW with post-processing options. Reason being is that I constantly switch between video's and stills, yet with video's - it's a lot less obvious to modify white-balance after shooting. Nonetheless, the camera uses the configured whitebalance for both stills & video's.
Is there an option to assign one of the buttons -or an easy to access shortcut, or pressing a button for a longer time- to immediately set (and apply) the custom whitebalance? It would basically switch to the configure whitebalance option, 'capture' the white object you are pointing at and optionally immediately apply that whitebalance.