A psychophysical experiment was performed to determine the color that had the appearance halfway between two other colors with equal chroma and separated by either 40° or 60° of hue angle. Four color centers were used and a QUEST threshold procedure was employed to find the midpoint between two flanking colors. Rather than choosing colors that shared the same chroma attribute as the flanking color pair, observers chose colors that had less chroma and were closer to the midpoint of the line connecting the flanking pair in Cartesian coordinates. In a separate control experiment using the same stimulus configuration but a different set of instructions, subjects determined the color between the flanking colors that had the same chroma. In this experiment, subjects were able to choose the color with the same chroma as the flanks. The results of this experiment are discussed in relation to the usefulness of defining color appearance attributes.
Ethan D. Montag, "The Color Between Two Others" in Proc. IS&T 11th Color and Imaging Conf., 2003, pp 294 - 300, https://doi.org/10.2352/CIC.2003.11.1.art00051