When taking shots underwater, the water soaks up certain colours and the deeper you go the worse it becomes. That is why it looks as though you have a colour filter on. You can easily bring back the true colours using colour balance on photoshop. You will be amazed how much better the photo can look in seconds. This is essentially what underwater mode does on cameras anyway so it certainly is not cheating. Give it a try.

remember though author, any changes you make, must affect the whole shot, not just selective parts of it.