I have a 1955 RCA 21CT55 and a 1963 Zenith 29JC20 restored and both produce good color pictures. Here are links to the restoration threads with pictures of the results:
RCA 21CT55
http://videokarma.org/showthread.php...=21ct55&page=5
Zenith 29JC20
http://videokarma.org/showthread.php...=29jc20&page=7
The RCA 21CT55 has wideband color demodulation so you can see finer detail in the color. Its early CRT has dimmer phosphors but really nice colors. The fine tuning has to be adjusted carefully to minimize color and sound IF interference visible in the picture.
The Zenith has the 21FJP22A with rare earth phosphors that are brighter and good color, but I prefer the 21CT55 color. The Zenith has the narrow band demodulation so its has a softer color picture than the RCA. The fine tuning is much more forgiving than the 21CT55.
I like both of them very much. I tend to watch the Zenith more, mainly because I feel it does not push its components (such as the flyback) as hard as the RCA. I have installed low speed cooling fans on both sets flybacks, just in case. The Zenith flyback runs cooler than the RCA.
Dave