The underlying physiological mechanisms involved in color opponency include the bipolar and ganglion cells in the retina, which process the signal originated by the retinal cones before it is sent to the brain. Models like RGB are based on what happens at the lower, retinal cone level, and thus are fitted for presenting self-illuminated, dynamic images as done by TV sets and computer displays; see additive color. The NCS model, for its part, describes the organization of the color sensations as perceived at the upper, brain level, and thus is much better fitted than RGB to deal with how humans experience and describe their color sensations (hence the "natural" part of its name). More problematic is the relation with the CMYK-model which is generally seen as a correct prediction of the behavior of mixing pigments, as a system of subtractive color. The NCS coincides with the CMYK as regards the green-yellow-red segment of the color circle, but differs from it in seeing the saturated subtractive primary colors magenta and cyan as complex sensations of a "redblue" and a "greenblue" respectively and in seeing green, not as a secondary color mix of yellow and cyan, but as a unique hue. The NCS explains this by assuming that the behavior of paint is partly counterintuitive to human phenomenology. Observing that the mix of yellow and cyan paint results in a green color, would thus be at odds with the intuition of pure human perception which would be unable to account for such a "yellowblue".