Specifically, conventional B&W papers are insensitive to red, which of course is present in most color negatives.
The "special papers" to which David refers are the Kodak Panalure line. It seems to have vanished from store shelves before other Kodak B&W papers, but if you're lucky you might still be able to find some somewhere. (I noticed an eBay auction for some a week or two ago.) Panalure is sensitive to red as well as to blue and green, so it produces better results from color films, at least in theory and if you want to match what you'd have gotten with B&W film in the camera. The red sensitivity also means that you've got to treat it like a color paper with respect to safelighting. (Panalure is developed in conventional B&W chemicals, though.) AFAIK, no other manufacturer makes anything akin to Panalure.