Suppose we train bees to come to a red card,and having done so,we put the red card on the table in the garden among the set of different grey cards. This time we find that the bees mistake red for dark grey or black. They cannot distinguish between them.

• 假如我们训练蜜蜂飞向红色卡片，这样训练之后，我们把红色卡片放到花园里桌子上那套深浅不同的灰色卡片中间，这时我们发现，蜜蜂错把红色当成深灰色或黑色，而不能区别它们。