Hering argued that yellow is not a "redgreen" but a unique hue. Colorimetrist Jan Koenderink, in a critique of Hering's system, considered it inconsistent not to apply the same argument to the other two subtractive primaries, cyan and magenta, and see them as unique hues as well, not a "greenblue" or a "redblue". He also pointed out the difficulty within a four color theory that the primaries would not be equally spaced in the color circle; and the problem that Hering does not account for the fact that cyan and magenta are brighter than green, blue and red, whereas this is, in his view, elegantly explained within the CMYK-model. He concluded that Hering's scheme fitted common language better than color experience.