The situation is where he sees the blue, say, behind the mirror.

The active conditioning events are the events whose characters are particularly relevant for the event (which is the situation) to be the situation for that percipient event, namely the coat, the mirror, and the state of the room as to light and atmosphere.

The passive conditioning events are the events of the rest of nature.
In general the situation is an active conditioning event; namely the coat itself, when there is no mirror or other such contrivance to produce abnormal effects.

But the example of the mirror shows us that the situation may be one of the passive conditioning events.

We are then apt to say that our senses have been cheated, because we demand as a right that the situation should be an active condition in the ingression.
This demand is not so baseless as it may seem when presented as I have put it.