Here is an example.
A kindergartner teacher asks the class to point out anything in the room that is not red.
The first student says the white board. The teacher agrees, the white board is white and it is in the room.
The next says his pencil. The teacher agrees, the pencil is yellow, and it is in the room.
The third student says her notebook. The teacher agrees, the notebook is green, and it is in the room.
The fourth says the air. Do you agree? Is the air red? The air is in the room. However, it isn't a color, but the question wasn't to name a color other than red, but anything that is "not red" and in the room. The air, to me, fits that description, the student was correct.