There are red filters and there are underwater red filters. Usually the underwater ones are more orange than red. I took a gamble by ordering one on eBay that showed an orange filter with the word Dive on the side. When it arrived, it was a plain red filter, which I've had experience with before. It just makes everything red, not solid red, but very tinted red.
Although I don't have a TG, an underwater mode is your best bet. I use a Canon G12 and with its underwater mode, I get pretty good colors. Obviously, after 15m or so, the amount of red light will be so diminished that underwater mode won't be enough.