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

I would suggest drifting as the most likely siuation, although without
full information it is hard to be certain.

We get the same situation in reverse here.

Our bees are mainly blacks, but from time to time we experiment with
other types. Occasionally we try out a few yellower ones.

Once the colony(ies) with yellow bees becomes established and the
progeny of that queen begin to fly it is not long before you can spot
some yellow bees in more or less every colony in the apiary. There are
generally more of them the closer you are to the yellow colony, but they
can crop up anywhere, particularly near ends of rows or nearest the
current nectar source. These are not robbers or the result of cross
matings, they are just bees going about their everyday business having
adopted a home other than that in which they were raised.

Drones seem to have very little colony loyalty at all, and congregate
strongly in any colony raising queens.

If your bees are all of one general type you probably never notice this
phenomenon, but throw in a colony of radically different colour and it
is immediately plain.

In the UK it is often said that Italian bees are great robbers, but the
dominant bee, at least in eastern Scotland, is black. Thus it is obvious
if yellow bees are frequenting your dark hive, but not at all obvious if
the visitors (or adopted residents) are identical in colour to the hives
own bees.
--
Murray McGregor