Killer Minus Violet filter?

Hi all

I need your help to make an important decision. I've been using a
(free)Celestron Yellow No8 filter with my CR150HD 6" f/8 refractor
from the very first night. By now I really ought to be considering
something a little more sophisticated. But I read horror stories of
unnatural colour casts and worry about light loss due to unwanted
light pollution filtration. Pre-purchase nerves are making the
decision very difficult. There might be 50 quid at stake here! ;-)

BTW: It has to be waterproof to 6 Atmospheres. You would *not* believe
my dew. :-)

So what's the word on the street? Which is the killer minus violet
filter of the moment?

Thanks in advance
Chris.B