Achromatic settings are known to vary more along bluish-yellowish axes than reddish-greenish, following roughly the daylight locus of natural illuminants. We explored an additional asymmetry along the blue-yellow dimension, in which “blue” stimuli appear much more desaturated than their “yellow” complements. These differences were quantified with both a color naming task, which mapped out the gamut of chromaticities that appeared gray, and by a saturation matching task between pairs of opposing chromatic axes. The losses in blue saturation appear strongest when the colors are presented as luminance increments. They are inconsistent with chromatic aberration because they persist with uniform fields. They are also inconsistent with cone-specific (e.g. S cone) nonlinearities, because they are stronger along the blue-yellow axis (−45 deg in the LM vs S plane) than along an axis with the same component cardinal-mechanism contrasts combined in opposite phase (+45 deg in the LM vs S plane). This suggests a post-receptoral site for the effects. The blue-yellow asymmetries can have a surprisingly large effect on perceived color. For example, images of tin or silver objects - which appear largely achromatic - become distinctly copper or gold when displayed with the equivalent complementary chromaticity. They may also explain why photographic negatives (e.g. of faces) sometimes appear conspicuously less colorful than their positive counterparts, even though they contain an equivalent gamut of chromaticities. Supported by EY-10834