Imaging systems tend at first to simulate the opponent yellow and blue vision channels (YB) even if that perceptibly violates trichromatic simulation of opponent red and green channels (RG). The preference is biologically traced: 8% male population are deficient in RG vision and only 0.003% in YB vision. The YB pair is not the usually assumed alternating combination of M, L, and S-cone responses (say, L+M-S): it is independent of RG sensations (L-M). The complementary yellow (570) and blue (465 nm) are seen after the RG pair has disappeared with decreasing illumination. The yellow is not seen after the 650-nm sensitivity limit of rhodopsin even if the red is over 50 nm more. The ‘blue-cone monochromats’ and some protanopes, having no M and L-cones, see the YB pair. Yellow adaptation eliminates the YB sensations but hardly influences the RG pair. Reflectometry of living retinas shows the ‘M and S-cone pigments’ rather to be long-living products of iodopsin (L-pigment) and rhodopsin.