If you can get a small secondary dive flashlight. (Not expensive) and shine it on the targeted photo subject, it will help show more color. You start losing colors from the spectrum as you go deeper that's why the nice UW cameras have the lighting setups (at least to my knowledge) Many divers carry flashlights in order to see the true colors of deeper water fish and coral. If there is a small target that you'd like to photograph, try the flashlight.