The colour of the bees in the hive can originate from any one or combination of the following.
- When the queen mates she mates with multiple drones. The drones in the air at the time ideally have genetic diversity, one of which is colouring. As she lays out the brood nest, she uses up the sperm from those drones. In this way the characteristics of the bees in the hive is dynamic. Meaning a hive changes over time, from one brood cycle to the next. The bees colour changes, temperament changes, productivity changes, resilience changes. The queen may have been using up a dark drone sperm and now she is into an orange ones.
- Bee drift. Any apiary that has more than the one hive in the area will have some bees drift between hives. This includes nearby feral colonies. A bee may lose her way, or the beekeeper moved her hive, the beekeeper may have caused mayhem during inspections or blocked their entrance, or a wind gust blows her landing approach over to the next entrance. Tired, or cold, or coming in hot and heavily loaded, she will go into any closest entrance that will have her. A hive of otherwise black bees can pickup orange ones, and vice versa. This is a normal and regular occurrence. Goes on alot more than you may think.
- Robbing. Depending on the time of year, seeing different coloured bees in a hive could be those scouts or the stealth robbers. Robbing does not always instigate a flurry of activity and/or fighting. Sometimes it is remarkably subtle and covert.
- Absconding / Invasion. A nearby hive may be sick, queenless, broodless, or pest infested. The bees from there know the condition is intolerable, unmanageable, or terminal. They simply leave and look for a new home. They may beg into other hives, trickling in. Or they may move/invade en-masse.
FYI - I see the most changes in colouring of bees in the spring and in the fall. These are times that drifting / absconding / robbing are most apparent. As a result these are also the times of highest transmission of pests and diseases between colonies, and thus why regimented inspections and treatments during those seasons are so important. For the reasons present in all of the above, do not be complacent nor surprised by a healthy strong hive that suddenly becomes sick or infested during those seasonal periods. When you are seeing changes in your bees, be happy of the diversity in the hive! Yet at the same time, be cautious and guarded. Let that change also be a trigger to be looking for possible emergence of new pests / diseases in the hive in the near future.
Hope that makes sense and hope that helps!