on perceivers, but it also often called simply dispositionalism – various forms of course exist). An example of a notable theorist that defends this kind of view is the philosopher Jonathan Cohen. Another type of reductionism is color physicalism. Physicalism is the view that colors are identical to certain physical properties of objects. Most commonly the relevant properties are taken to be reflectance properties of surfaces (though there are accounts of colors apart from surface colors too). Byrne, Hilbert and Kalderon defends versions of this view. They identify colors with reflectance types. A reflectance type is a set, or type, of reflectances, and a reflectance is a surface's disposition to reflect certain percentages of light specified for each wavelength within the visible spectrum. Both relationalism and physicalism of these kinds are so called realist theories, since apart from specifying what colors are, they maintain that colored things exist. Primitivism may be either realist or antirealist, since primitivism simply claims that colors aren't reducible to anything else. Some primitivists further accept that, though colors are primitive properties, no real or nomologically possible objects have them. Insofar as we visually represent things as colored – on this view – we are victims of color illusions. For this reason primitivism that denies that colors are ever instantiated is called an error theory. Color discourse If color fictionalism is true, and the world has no colors, should one just stop color discourse, and all the time wear clothes that clash with each other? Prescriptive color fictionalism would say no. In prescriptive color fictionalism, while color discourse is, strictly speaking, false, one should continue using it in everyday life as though color properties do exist. Color vision became an important part of contemporary analytic philosophy due to the claim by scientists like Leo Hurvich that the physical and neurological aspects of color vision had become completely understood by empirical psychologists in the 1980s. An important work on the subject was C. L. Hardin's 'Color for Philosophers,' which explained stunning empirical findings by empirical psychologists to the conclusion that colors cannot possibly be part of the physical world, but are instead purely mental features. David Hilbert and Alexander Byrne have devoted their careers to philosophical issues regarding color vision. Byrne and Hilbert have taken a minority position that colors are part of the physical world. Nigel J.T. Thomas provides a particularly clear presentation of the argument.