Three dimensions of aperture color do not suffice some professional applications of color imaging. To improve metameric and low-illumination subject colors, a fourth spectral channel in color films and the multi-spectral systems in the electronic imaging are designed. To evaluate the dimensionality, a mathematical simulation has been performed on the base of the optical mechanism for single-pigment intrareceptor color opponency, which explained color phenomena, inconsistent with the common RGB-cones opponency models. Recent data on the two anatomical parts of outer segment of rod or cone and the spectra of long-living photoproducts at the human body temperature allowed to detect five spectral ranges independently affecting color hues within a wide illumination range. The rhodopsin partial receptors (505 and 535 nm) in the rod perform the yellow-blue separation in the two differential sensitivity ranges parted by the neutral point of protanope or deuteranope at 495 nm. The partial receptors (560 and 610 nm), based by the cone photopigment, did the green-red separation in the three ranges of visible spectrum parted by the neutral points of tritanope at 460 and 575 nm. At least a fourth independent channel has been shown to be required to provide simultaneously all of the colors in a scene for the spectrally-correct reproduction.