When we obey the order, “Observe the colour … ”, what is we do is to open our eyes to colour. “Observe the colour … ” doesn't mean “See the colour you see.” The order, “Look at so-and-so”, is of the kind, “Turn your head in this direction”; what you will see when you do so does not enter this order. By attending, looking, you produce the impression; you can't look at the impression.