[infinity]

The argument does not state that Bertie really sees a green object in the sense that light with green wave lengths enters the eye and triggers biochemical reactions.

The argument talks about the experience of "greenness" as the after-image of a red object:

  Suppose Bertie is experiencing a green after-image
  as a result of seeing a red flash bulb go off;
  the greenness of the after-image is the quale.

Indeed, there is no green object outside or inside of Bertie. The light bulb was red, the memories or patterns in the brain are not green.

  Sensory qualities pose a serious problem for materialist
  theories of the mind. For where, ontologically speaking,
  are they located?

The argument is about materialist theories of the mind. After the argument, which seems to me a valid argument against oldschool hardcore materialism (a material location for the greenness is needed), the following paragraph mentions a more modern development, namely the modern representational theory of sensory qualities, sometimes as an attempt to resolve the foregoing dilemma compatibly with materialism.