What it teaches
Sorting a palette into warm and cool. It is the first idea in art that is about how a colour feels rather than what it is called, and it is the one that explains why a picture has a mood.
Children agree with each other about this almost perfectly without ever being taught it, which makes it a rewarding thing to be asked.
What to look for
Ask which colours a picture in the room uses and how it makes them feel. That is the whole of this idea, and it takes one question.