Colored shadows are observed when two differently colored lights are combined in twilights. When both lights add to an equi-energy white 'balanced' spectrum, the hues of the shadows show regular opponent colors, being reciprocals of the colors of the lights. When a white and a colored light in a twilight add to an 'unbalanced' spectrum, the hues of the shadows result from the same laws of opponency and reciprocity, but the eyes see "what they have optically calculated" instead of seeing "what really (physically) there is". At adaptation to the colored light, unbalanced states in physics become physiologically re-balanced by diffractive-optical chromatic resonance, guaranteeing color constancy at variations of illuminants. Colored shadows can be interpreted as serial products of diffractive 3D grating-optical von Laue interferences and of optical cross-correlations between local and global information in the human eye. The human eye's hardware, with diffractive-optical multi-layer gratings in aperture and image space, represents an illuminant-adaptive diffractive-optical RGB Color Sensor guaranteeing color space normalization towards RGB equilibrium states (RGB white norms) in reciprocal grating space.
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