  Locke’s description of this inverted spectrum scenario is laden with his own commitment to “Ideas”, which (on one interpretation) are sense-data, some of which possess both color and  shape.[13]  On this view, spectrum inversion is a case of “sense-datum inversion”: when Invert looks at a violet she becomes acquainted with the kind of sense-datum Nonvert is acquainted with when he looks at a marigold. Setting this tendentious theoretical gloss aside, Locke’s scenario has three notable features. First, it is a case of spectrum inversion from birth. Second, it is a case of inversion within the same linguistic community. Third, it is (or is naturally read as being) a case in which Invert and Nonvert are behaviorally alike—a behaviorally undetectable spectrum inversion.