So, the issue when taking pictures is that under the amount of blue light we all run it falls outside of the "normal" expectations for a camera to display the color white and make adjustments. This is why everything is blue when you take a picture, if you can find a camera that has a settable white balance you can teach your camera what "white" is, you do this by placing something pure white in the tank up against the glass, then you tell your camera "this is white" then the camera can figure out all the colors accurately. What Jim did was place a yellow filter in front of the lens, look at any color wheel, the opposite of blue is yellow, so essentially your shifting your white balance with the filter. now placing any random yellow tinted lens will get you close, a pair of yellow tinted sun glass's will get you a better picture.
BTW Jim, extremely impressive pictures, those are beautiful corals.