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Four-tube cameras are good for getting a good monochrome picture, and for getting good detail in the color picture (eliminating loss of detail due to misregistration). BUT, the color will never be as true as a three-tube camera unless the low-frequency luminance is derived from the three color plumbicons (because Y = L^(1/gamma) is not the same quantity as Y= .3R^(1/gamma) + .59G^(1/gamma) + .11B^(1/gamma).
RCA published a paper showing that the color errors were not too bad, but nevertheless, the tendency would be to lighten saturated reds and blues on a normal NTSC receiver. This could be compensated somewhat by deliberately pulling the blacks lower in the luminance tube channel I suppose (or by modifying the luma tube optics to favor green), but the three tube camera by comparison could have more accurate color.
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