The psychologist George Boeree, in the tradition of J. J. Gibson, specifically assigns color to light, and extends the idea of color realism to all sensory experience, an approach he refers to as "quality realism". Jonathan Cohen (of UCSD) and Michael Tye (of UT Austin) have also written many essays on color vision. Cohen argues for the uncontroversial position of color relationalism with respect to semantics of color vision in Relationalist Manifesto. In The Red and the Real, Cohen argues for the position, with respect to color ontology that generalizes from his semantics to his metaphysics. Cohen's work marks the end of a vigorous debate on the topic of color that started with Hardin. Michael Tye argues, among other things, that there is only one correct way to see colors. Therefore, the colorblind and most mammals do not really have color vision because their vision differs from the vision of "normal" humans. Similarly, creatures with more advanced color vision, although better able to distinguish objects than people, are suffering from color illusions because their vision differs from humans. Tye advanced this particular position in an essay called True Blue. Paul Churchland (of UCSD) has also commented extensively on the implication of color vision science on his version of reductive materialism. In the 1980s Paul Churchland's view located colors in the retina. But his more recent view locates color in spectral opponency cells deeper in the color information stream. Paul Churchland's view is similar to Byrne and Hilbert's view, but differs in that it emphasized the subjective nature of color vision and identifies subjective colors with coding vectors in neural networks. Many philosophers follow empirical psychologists in endorsing color irrealism, the view that colors are entirely mental constructs and not physical features of the world. Surprisingly, most philosophers who have extensively addressed the topic have attempted to defend color realism against the empirical psychologists who universally defend color antirealism. Jonathan Cohen has edited a collection of essays on the topic of color philosophy called Color Vision and Color Science, Color Ontology and Color Science. Inverted spectrum The inverted spectrum is a thought experiment dating back to John Locke's An Essay Concerning Human Understanding. It uses color to discuss the nature of qualia. As explained by Locke: Color fictionalists argue that, since we can imagine perceiving an inverted color spectrum, it must follow that color represents a property that determines the way