This paper argues that the distinctiveness of the Hering primary hues – red, green, blue, and yellow – is already evident at the retina. Basic features of spectral sensitivity provide a foundation for the development of unique hue perceptions and the hue categories of which they are focal examples. Of particular importance are locations in color space at which points of minimal and maximal spectral sensitivity and extreme ratios of chromatic to achromatic response occur. This account builds on Jameson & D’Andrade’s (1997) insight about the relationship between the Hering primaries and chromatic/achromatic ratios, Romney & Chiao’s (2009) color appearance model, and Thornton’s (1971; 1999) research on artificial lighting.