Other possibilities, in a myriad of possibilities!
Honey bees and bumble bees will often  collect, in addition to pollen,
brightly colored fungicidal powders that
are applied to their host plants. I remember one type of fungicide being
BRIGHT RED. The pollen loads the
bees carried were deep vermilion. You should also be cautious of
pollination biologists using brightly
colored pollen analogues (dyes, most often) in their field experiments.
        I have also observed honey bees collecting catkin pollen when
nothing else is available. In addition to being very colorful, catkin
pollen is noticeably abundant early on. Honey bees may also collect inert
particles that have the same consistency of pollen, these my be used for
building materials, perhaps propolis. Also, some wild bees are partial to
particles of freshly sanded paint.
 
Anyway, this discussion will undoubtably add insult to injury.
 
 Good hunting all...
                                                Discombobulatingly Yours,
                                                Blair
 
Blair J Sampson
Dept. of Entomology
Auburn University
Auburn, Alabama 36849-5413
U.S.A.
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