1. First off nothing gets destroyed when using filters; you are just compensating for lack of color. Unless you back light, which will show the filters color, or overcompensate, the colors will seem neutral until they go to black.
For photography if you are using strobe the natural colors will show within your strobe range since they flash at 5600 degrees (sunlight).
As for no strobe stills and film...
Look at an opposing color chart and depth color loss to figure out how to filter.
For stills, you can do the corrections in post i.e. separate background from subject, so try to filter for the subject.
For film just try to balance the color unless you are going for the florescence qualities of the subject in which case you match the color loss to bring out the florescence, i.e. use a blue filter in blue water or a green filter in green water.
2. For green you would use a magenta filter. For blue you would use a yellow filter with some red in it, i.e. color temperature straw (CTS).
If you over correct the subject will still show well, but your background will match color, especially if back lit.
3. In general most do not use a filter for strobe unless you are trying to do something a little more artistic (which you should definitely experiment with). You could even try to gel your strobe, which would have a more minor effect considering the light is traveling through it and splashing the subject. This could be very interesting and is something very few underwater photographers do.
Remember, all photography and cinematography is beautiful. There is always something special in it whether it is is the subject, background or foreground. Get out there and shoot as much as possible, and the images will grow with you're imagination.
Hope this helps, and good luck!
Whatever you can do, or dream you can,
begin it. Boldness has power, genius and magic in it.
Begin it now."
--- Goethe
