Pipe cleaners are used to clean the stems of tobacco pipes. They are basically just two lengths of twisted metal wire wrapped around some cheap tufts of fabric. Pipe cleaners are usually white . . .
. . . but they do come in a great variety of colors.
Someone who is using pipe cleaners to actually clean the stem of his or her pipe will want white ones, so that they can judge how much of the tar they are getting out of the pipe stem. In this case, black pipe cleaners make a lot of sense, since they will be using them to collect pollen, which would show up much better on a black pipe cleaner.