This paper describes the architecture for a color picture tube (CPT), which enables a cost-effective expansion of the color gamut. Besides a gamut expansion based on application of more-saturated phosphors in the present three-primary system, four- and five-primary systems are described. Gun-pitch modulation allows the application of a conventional electron gun for both a four- and five-primary CRT. In these systems, the mask and matrix transmissions need to be reduced to maintain color purity. From this point of view, a five-primary CRT is unrealistic. Two four-primary CRTs are evaluated in more detail. But, here, the total anode current to generate white has to be increased substantially because of the reduced mask and matrix transmissions. Nonetheless, in this paper it is argued that with one of the four-primary CRTs more-saturated yellow colors can be displayed at 85% of the display luminance of a conventional system without loss of perceived sharpness.