I can't recall the picture, but it is probably one of the fluorescent
powders that many pollination biologists here use to mark insects or mimic
pollen.  Sources in the U. S. include Day-Glo Color Corp., Radiant Color
Corp., and Shannon Luminescence.  Particle size is about 5-6 microns, price
about $7/pound from manufacturers (if they will sell that small an amount),
more from retailers.
David Inouye