This difference would be important if he were looking at a star whose colour was Cambridge blue.

The star might have ceased to exist days ago, or even years ago.

The situation of the blue will not then be very intimately connected with the situation (in another sense of 'situation') of any perceptual object.

This disconnexion of the situation of the blue and the situation of some associated perceptual object does not require a star for its exemplification.

Any looking glass will suffice.