Robert Brenchley asks:  "Could this be a case of a queen having mated with
drones of different races, and producing different coloured offspring?"

Yes, that is the most likely explanation.  Of course a queen usually mates
naturally with many drones, so there will be a number of cohorts of bees in the
hive that will be half sisters.  Not only may they have different habits and
behaviors, but they also can be phenotypically different.  I had a hive of
Italian bees (my first hive) that superseded the queen, and after the new queen
started producing offspring in earnest, about half were the yellow Italian and
half where dark German (as we call them here).  By deduction, it was obviously
a case of the new queen having mated with drones of different races.  The bees
don't care.  They are all half sisters with the same mother.  It may result in
the overall hive exhibiting a greater range of behaviors and can have positive
results if the behaviors exhibited are desired behaviors.

Layne Westover, College Station, Texas, U.S.A.