I decided to try getting the real color of that anemone during another dive after I posted here.
I had a wide angle lens and magic filter when we were diving there with a different route. I had chance to get down to that location with around 2 minutes non deco bottom time.
I spent almost half of it trying to make custom white balance however my D200 failed. Than I decided to shoot and making white balance afterwards. (with this purpose i shot my hand too)
I took several shots while the anemone fish absolutely not be corporative and swimming elsewhere instead of being in front of the anemone till the end of my non deco bottom time.
Even though the attached photo is far from being an example of a good composition the color of the anemone is totally the same as it looks there at ~30meters. It is shot without any strobes. Even The fish is with underexposure while anemone glowing there has a contrast with surrounding objects.
I think it would be possible to get a good shot with a new generation SLR with higher low ISO performance and with a macro lens with a magic filter on.
On the other hand i think the anemone fish would still be underexposed if the exposure shall be based on anemone :-/
