Note more expensive "black screens" are often an improvement for projection in a brightly painted or light leaky room.
I've seen cabinet games that used the mixed color set in monitor board labeling. Some as MCY, MCG, you name it.
The context is normally there for a electronic tech. (could've been poor translation too) (not a counterpoint so much as a possible explanation; color wheel exactness isn't always that important there, the label text won't change the final output of the equipment....parts might 
Stage gel companies used both descriptively. E.g. Magenta was red, but red was more red; so I imagine some of that spread into projection TV lamp sets too. I never looked to mixed lamps to find out. (secondaries, Magenta, etc, is warmer and more natural looking imo)
