Bill suggested marking the queens. This will allow to find her quickly, and also to track her over the years. This year the mark is white. Other years it will be a different color. So beekeepers with several or many hives can track the age of their queens. They can then decide to replace a queen to rejuvenate a colony.
  The first task is to find the queen. It has about the same shape as the workers but it is larger. It may sound easy, but in fact involves pretty good looking. In one situation, we missed the queen and had to go back over the frames to find it. Here is me taking a closer look at one of the frames full of bees. Bill is on my right also taking looks.

Both of us searching for the queen of this colony.

Once we have found a queen, then Bill traps her with this little cage. The queen doesn't like it too much and runs around. Bill actually has to pin her down to get a drop of paint on her thorax.

Here we can see the queen right under the brush. The dark part is the thorax and head. The body extends to the right (from viewer).