I think the reference on p. 28 is pointing out that the brain doesn’t turn purple (and a purple brain wouldn’t help anyway, as there are no eyes in the brain to see the purple). The remainder of the page is extending the example to further elaborate the problem of subjective experience.
I cannot find the reference to qualia quoted in The Taboo of Subjectivity at all—p. 74 is before Dennett even defines qualia, and p. 374 does not have those exact words—only the conclusion of a thought experiment illuminating his rejection of the concept.
Belatedly:
I think the reference on p. 28 is pointing out that the brain doesn’t turn purple (and a purple brain wouldn’t help anyway, as there are no eyes in the brain to see the purple). The remainder of the page is extending the example to further elaborate the problem of subjective experience.
I cannot find the reference to qualia quoted in The Taboo of Subjectivity at all—p. 74 is before Dennett even defines qualia, and p. 374 does not have those exact words—only the conclusion of a thought experiment illuminating his rejection of the concept.