All of the single gun early color tubes, including the RCA 1950 prototype, suffered from very low brightness, since they depended on a single gun to illuminate three color phosphors.
As far as the 1954 Zenith rectangular color set,
http://www.earlytelevision.org/zenith_rectangular.html
there is no surviving sample. We have a CBS Hytron 22 inch rectangular tube on display,
http://www.earlytelevision.org/color_crts.html
and there is also a Westinghouse 22 inch tube that was supposedly not built by CBS, but looks very similar. Three Westinghouse and CBS sets with these tubes may be around, but we've never gotten photos of them.
http://www.earlytelevision.org/21_inch_color.html
Finally, there is a photo of a DuMont rectangular tube, from 1954, but no surviving example.
http://www.earlytelevision.org/dumont_color_crt.html
(bottom photo)