With a digital camera, I'd avoid any filters. Using filters underwater presents a whole bunch of other problems you'll have to deal with, not the least of which is sucking precious light away from your sensor. You can get better results by applying the color correcting filter afterwards in the computer. The filters are pretty handy for underwater film cameras. But you kind of have to know what you're going to shoot and under what conditions you'll be shooting to know which ones to use.