Several recent messages have said that they couldn't recall where the original
reference to bees stinging dark colors and certain textures was located. The
original paper, by John Free, was published in Animal Behaviour in 1961 (The sti
   muli releasing the stinging response of honeybees, Anim Behav 9: 193-196). If
 
you want to see a review of the literature on stimuli that release stinging,
there is one in an article of mine in the Journal of Apicultural Research
(Measurements of stinging behaviour in individual worker honeybees (Apis
mellifera L), JAR 28: 71-78, 1989).
        One recent suggestion was that CO2 in smoke might be making bees less
aggressive, and the note asked if anyone had tried a dilute CO2 source in
place of smoke. I would advise against that very strongly. Evidence suggests
that CO2 makes honey bees (and some wasps that have been studied) more likely
to sting (see the "breath test" of Boch and Rothenbuhler, 1974, Defensive behavi
   our and production of alarm pheromone in honeybees, Journal of Apicultural
Research 13: 217-221). Probably it is yet another cue (along with dark color and
    furry texture) that would normally be associated with a vertebrate predator
opening a hive.
        As for what you place in a smoker, in my recent stay at a Dutch
University, I learned that Dutch and German beekeepers favor burning strong
tobacco in special pipe-like smokers. I tried it, it does calm the bees,
although the amount of smoke involved and its components left me feeling a
bit ill. A friend of mine in Connecticut always burns pieces of old blue
jeans, which also smells bad but works. So, I'd guess that bees aren't too
particular on this point.