In reply to Phantom Disliker:
Because, we have defined smell as the thing we experience when certain receptors in our nose interact with certain molecules. Similarly, BB describes light as having no colour, and IIRC, sound waves as having no sound. These cases are exactly the same. If the logic of the book is extended to sound, as you suggest, then the tree doesn't produce a sound in the absence of an ear, it produces a pressure wave. Likewise light doesn't have a colour, it is just light of a given wavelength. But the fact is, wavelength, chemical structure, frequency, are simply phenomena that we perceive as colour, odour, and pitch, respectively. So to suggest those properties don't exist is just a slightly odd and irrelevant point. The point is much better made by simply stopping after expressing, as the author does, that the way our brain makes sense of those physical properties/phenomena is amazing, without going onto this bizarre argument that molecules don't smell, or that light doesn't have a colour. They intrinsically do have those properties, because we have defined those properties as resulting from physical phenomena.