 First, consider the phenomenological distinction between unique and binary hues. Some colors appear to incorporate other colors, and some do not. Purple, for instance, appears both reddish and bluish; red just looks red. Some philosophers contend that the leading physical theories of color cannot explain the unique-binary distinction without essentially invoking the color experiences of subjects. How, for instance, do reflectance classes identified with unique hues differ from those associated with binary hues?