Okey doke on the RAW but...uh, nevermind. On the filter biz: I've seen FantaSea type glass filters that slip externally over Canon housings (at least the G series housings) that run around $100 bucks, not sure if they have the same thing for S95s. Inon and Dyron have adapters that would hold filters for the S95 Canon housing. These would let you remove the filter uw if necessary. (I believe if you got an Inon or Dyron wa lens the same adapter/holder should hold the filters.)
You might consider using gels or glass filters on the inside of housing, lot's cheaper. Drawback is you have to decide before closing the housing if you are going to use a strobe, given that the strobe is a "near daylight" color balance. (ie--means you wouldn't use, say, a "magic" filter in combination w/ strobe) Places like B&H Photo Video or Adorama have gels. The old "Wratten 25" designation would get you a red filter, in case they don't list gels by color name. Be aware, gels are not water friendly! // ww