Robert sees different colored bees in the hive and asks "Could this be a
case of a queen having mated with drones of different races, and producing
different coloured offspring?"

Yes, that is exactly what is going on.  In fact, it is not at all uncommon.
If a beekeeper is breeding queens, seeing bees of the same color in a hive
is a sign that stray drones are not getting through.  On the other hand,
seeing different colors is a sign that more isolation is needed!

Lloyd
Lloyd Spear, Owner, Ross Rounds, Inc.  The finest in comb honey production.
www.rossrounds.com