One of the major problems in underwater photography is the loss of color as you descend. The water filters out the red end of the spectrum, creating the blue world all divers are familiar with.
Visually this is a problem, divers are unable to appreciate the beautiful colors of marine life without using an artificial light source. Most divers carry lights, even on daytime dives, for this reason. It can be quite dramatic to turn on a light and watch brilliant reds and yellows appear where there was little color without the light.
Photographically it is even more challenging, a strobe can light up nearby objects, revealing the colors. For more expansive scenes even the most powerful strobes fail, resulting in photographs heavy in greens and blue, with very little red. For some photos, the blue works, a “true” representation of what was seen. Often the blue does not work, the resulting photograph is an unattractive blue tinged with green, that no amount of fiddling in Photoshop will salvage.
One method in dealing with the loss of color balance is to simply take the loss further, convert the image to a black and white photograph. This is a technique you will see used in underwater photography quite often. By removing the distraction of color, the viewer is able to focus on the subject. The same reason so many modern photographers eschew color, even in an age when wonderful saturated colors are easily reproduced.