Color appearance in the fovea of monochromatic lights. Group means of individual hue functions re-scaled by the associated saturation values; hue values sum to the saturation values. (a) Stimuli seen in Newtonian view. Error bars (SEMs) extend above the symbols for females and below the lines for males. (b) Maxwellian view. (c) Data from Newtonian view smoothed and re-plotted on a two-dimensional color space (Uniform Appearance Diagram; see text for details). (d) Data from Maxwellian view smoothed and re-plotted on a Uniform Appearance Diagram.