Opponent channels must be calibrated to the average color of the scene (von Kries adaptation), which discounts illuminant changes and is an initial component of color constancy.

Evidence

Environmental Influences on Color Vision (M. Webster (via UC Irvine))

XREF: connects to: White is the most inferior of colors of morals of superiority. It follows that whiteness is the lack of characteristics that make a theme and give it its facets of colors. ; Because of adaptation, observers exposed to different environments should perceive color in significantly and systematically different ways, including differences in achromatic settings. — Normal variations in color vision V: Simulations of adaptation to natural color environments

Because of adaptation, observers exposed to different environments should perceive color in significantly and systematically different ways, including differences in achromatic settings. (similarity 0.90)
Perceived white reflects a response norm that varies with adaptation, and individual differences in perceived white shrink when observers share a common white adapting stimulus — the white point… (similarity 0.86)
Colors are not properties of objects but of perceptual processes, and one proposal identifies them with physical ‘spectral surface reflectance.’ (similarity 0.80)
In visual perception a color is almost never seen as it physically is, making color the most relative medium in art. (similarity 0.79)
There is generally no fixed relation between spectral distribution and perceived color, though a surface does have a determinable color under fixed viewing conditions. (similarity 0.79)