Is CMY just one-minus-RGB?
In a theoretical subtractive system, CMY filters could have spectral absorption curves with no overlap. The colour reproduction of the system would correspond exactly to additive colour reproduction using the red, green and blue primaries that resulted from pairs of filters in combination. Practical photographic dyes and offset printing inks have spectral absorption curves that overlap significantly. Most magenta dyes absorb mediumwave (green) light as expected, but incidentally absorb about half that amount of shortwave (blue) light. If reproduction of a colour, say brown, requires absorption of all shortwave light then the incidental absorption from the magenta dye is not noticed. But for other colours, the “one minus RGB” formula produces mixtures with much less blue than expected, and therefore produce pictures that have a yellow cast in the mid tones. Similar but less severe interactions are evident for the other pairs of practical inks and dyes. Due to the spectral overlap among
