>>The workers do not mix in the supers but work exclusively above their queen.
I think it's hard to avoid mixing. How did you come to this conclusion? You'd need to have a dark line in one colony, a light colored one in the other, and then check the bees in the supers.
Waldemar
****************************************************
* General Information About BEE-L is available at: *
* http://www.honeybeeworld.com/bee-l/default.htm *
****************************************************