Then I got an idea. Why not put a colored thumb tack on the outside of the hive telling me the color of the queen inside. I have few hives but if you had a lot and had marked queens it would make for a quick inventory of your queen ages without opening. Also, if you opened the marked hive and found an unmarked queen then you know you had a swarm occur and if so maybe rethink your management plan.
I found the thumb tacks at a CVS pharmacy and could not believe the colors included were exactly the colors used for queen marking. There is even a black thumb tack for using as an unmarked queen indicator. You get a ton of tacks and they are easy to throw in the equipment you carry.
When marking my hive I placed my tack on the corner of the outer cover and started finding it was also a good idea to put another one under the lip of the outer cover too. That way when the outer cover is flipped over on the ground during inspection you can see the color. My memory was so short I could not remember what the color was from the time it took to open. A hive tool can quickly change it out for another color if you change queens.
I was initially worried that the sun might bleach out the color or the weather rust them but neither occurred. I took samples of several tacks and put them on the side of my chicken coop in full sun exposure all summer and winter as a test. Their color held perfectly.