Calculated b and y chromatic response curves (b as negative portion, y as positive portion) for protanopes (P, in red) and deuteranopes (D, in green), redrawn from Hurvich & Jameson [35].

The curves intersect the zero line at 489 and 498 nm and their wavelength peaks are about 540 and 565 nm. Superimposed in gray are spectral sensitivity curves for M and L cones. In deuteranopia, yellow hues derive from the L cone curve (peak 565 nm) and its product the y chromatic response (see [36]), whose peak is also 565 nm. These are missing in protanopia and replaced by the M cone and its g chromatic response. All functions indicate shorter wavelength peaks and operating ranges for protanopia than deuteranopia.