In this paper, I shall evaluate a strategy recently used to try to demonstrate the impossibility of behaviorally undetectable spectrum inversion. After showing that the impossibility proof proves too much, I shall identify where it goes wrong. In turn, I shall explain why someone attracted to functionalist and representationalist assumptions might rightly remain agnostic about the possibility of inversion.

A version of the inverted spectrum thought experiment that disconfirms functionalism for the case of humans’ color experiences has typically been thought to require a certain kind of balancing act. What one needs, it has typically been thought, is a mapping of color experiences onto other color experiences that preserves the similarity and difference relationships among those experiences and the aspects of perceived colors underlying those similarities and differences. However, there are good reasons for being suspicious about whether that is (...) possible when the palette of color experiences is that available to humans with normal vision. The new version of the thought experiment constructed here doesn’t depend on preserving those relationships. I argue that there is a coherent, metaphysically possible scenario in which two human color experiences—any two—can be seen to be functionally equivalent. The upshot is that functionalism fails for all human color experiences. (shrink)