The philosophy of color is a subset of the philosophy of perception that is concerned with the nature of the perceptual experience of color. Any explicit account of color perception requires a commitment to one of a variety of ontological or metaphysical views, distinguishing namely between externalism/internalism, which relate respectively to color realism, the view that colors are physical properties that objects possess, and color fictionalism, the view that colors possess no such physical properties. History Philosophical concerns about the nature of color can be traced back at least as far as Anaxagoras (5th century BCE), who favoured color realism in his sophism: "Snow is frozen water. But water is dark in color. Therefore, snow is dark in color." Anaxagoras claimed that our perception deviated from the truth "...owing to the feebleness [of the senses]." Later, Democritus (circa 400 BCE) would say, "By convention sweet, by convention bitter, by convention hot, by convention cold, by convention color; but by verity atoms and void." In direct refutation of Anaxagoras, the Pyrrhonist philosopher Sextus Empiricus (circa 160 CE) noted that different animals would have different perceptions of color due to differences in their eyes, and that color was an attribute of a subject, and not the object itself. Theories of color One of the topics in the philosophy of color is the problem of the ontology of color. The questions comprising this field of research are, for example, what kind of properties colors are (i.e. are they physical properties of objects? Or are they properties of their own kind?), but also problems about the representation of colors, and the relationship between the representation of colors and their ontological constitution. Within the ontology of color, there are various competing types of theories. One way of posing their relationship is in terms of whether they posit colors as sui generis properties (properties of a special kind that can't be reduced to more basic properties or constellations of such). This divides color primitivism from color reductionism. A primitivism about color is any theory that explains colors as irreducible properties. A reductionism is the opposite view, that colors are identical to or reducible to other properties. Typically a reductionist view of color explains colors as an object's disposition to cause certain effects in perceivers or the very dispositional power itself (this sort of view is often dubbed "relationalism", since it defines colors in terms of effects