John A Tuttle wrote, "The 'dust' I've encountered has always been
either white or white with a slightly greenish or bluish tint."

When lead is cut with a knife, the fresh surface is very slightly blue
in color.  When exposed to normal atmospheric air, that surface quickly
combines with atmospheric carbon dioxide to form lead carbonate, which
is white.  This compound was used as the pigment for white paint since
the times of ancient Greece.  Lead in alternate oxidation states can be
red or yellow.

Many, many years ago in an undergraduate analytical chemistry lab we
did determine that the white powder that had accumulated on an old lead
pipe was in fact partially hydrated lead carbonate.

Bill Finch