Attached Link: Sea Chase

When I did this in Poser 4, I faked it. Even now, with Poser 6, I'd probably still fake it rather than spend days playing with render settings. I rendered with a single light dead overhead to simulate sunlight coming from the surface, and adjusted its colour to suit. Everything else was done in postwork. I restricted the colour range by desaturating, and faded the image to black at the edges, using a filter whose name temporarily escapes me. I believe it was a free download, though. I used a real underwater scene (photographed by me) as the background; that was also composited in postwork rather than rendered over.