Hey Dario,
I have the hero 2 and have used the polar pro red filter (
https://www.facebook.com/polarpro) It has made a massive difference to the underwater colour, making it more realistic to what you actually see when diving. That said, I've only tested it to 18m and if the sun is not out it tends to darken the recording. Also another problem is that when on the surface it turns the footage pink, so the new clip on filter cover looks favourable as it is snap on/off.
There must be a way to treat the footage in the edit studio but not quite worked this out yet!
When you come back to the mother land (UK) give me a shout, come stay for the weekend and we'll go spear some bass, if your still lurking in May I'll see you on the sunny side
Kev