It depends on what your idea of a "nice" cool tone is ...Originally Posted by ader
Are you mainly intersted in transparencies?
If you do your own color printing, it is relativey simple to change color balance in the enlarger. If you do not - you will have a problem with the "automatic color balancing" system used widely in "one-hour-labs" (see "Kodak Colorwatch"), no matter what flm or filtration you use - they will invariably try to make it "like everyone wants it". The only alternative is a "custom" color laboratory.
One book I will recommend - without reservation: "Filters - Special Effects, Accessories - From the Pros to the Pros" - the standard, usual, FREE catalog from B+W - the filter manufacturers. This has been my filter "bible" since - well, a LONG time ago ... and I haven't found anything better yet.
Check out your local Camera Shop, or a Professional Photographic Supply store... If they don't have them, I am sure you/ they can order them from Schneider/ Kreuznach.