There are 3 ways to improve the color balance for underwater digital photographs 4 if you consider post processing in Photoshop or a similar software.
1) custom setting the camera’s white balance using a white board slate. This isn’t easy even if your camera can do it. the slate needs to be set at the same distance and orientation as the subject. With subjects that move or a change in the light environment from things like schools of fish passing or clouds it becomes very hard to compose a shot.
2) Colored Filter lenses can fool the camera into changing it’s auto white balance and improve the general color quality. Althought the color improves you still need to get in close to the subject due to the water filtering the overal amount of light at depth.
3) Strobe/s The most effective way to improve color and the image depth is to bring the light to the subjects. Even small strobes improve color but they need to get in close to be effective. The farther away and larger the field of view the greater the need for more powerful strobes and sometimes multiple strobes. An additional advantage of multiple strobes is reduction and elimination of shadows. You should consider what your photographic desires and requirements are as it could require a considerable investment.