Was it on film?
It was the first one done in color - I’m not sure what you’re getting at, though. Do you mean that the media held up over time much better than other shows appeared to? 
Nope, Bonanza was not the first television series in color, not even the first filmed series in color. To give a well-known example of an earlier series, Adventures of Superman was in color from 1955 onward. Bonanza didn’t go on the air until 1959.
Hogan’s Heroes also looks great in high definition. It’s either INHD or HDNet that shows the series in its original 16x9 aspect ratio. It was filmed, of course.
Bonanza was distributed in color on video tape by NBC. Sorry I do not have the date when that began. My father worked at the local NBC affiliate.
Color televisions were expensive “back in the day” - so shows like Bonanza were almost tailor made for that demographic. I’ve noticed that the typical shot will have a green shirt, a purple scarf, red pants, a yellow curtain, etc. Gotta show off that new television!
Bonanza’s color was indeed a showcase for the process. Remember, it ran on NBC, which had a vested interest in selling color TVs, since it was connected with RCA.
Some other shows look faded or chalky. Maybe they were done with crapier film. Not everyone could afford Technicolor, and some of the other brands of film had different dyes.
Even Kodak had certain dyes that failed, and they were successfully sued because they had advertised “Memories that last a lifetime”
If you’re talking about the camera negative — not likely. Virtually all Hollywood studios shooting for network television series used color negative stocks made by Eastman Kodak, and the processing was done by the same major labs in Hollywood, usually Consolidated Film Industries. At no time did Technicolor create its own negative stock in 35mm. And after the three-strip Technicolor camera was retired in 1954, Technicolor was a print-making operation only, relying on the color negative stock of others — usually Eastman Kodak.
When television prints look bad, it’s usually because of an inferior print-making process. For example, the prints make have been struck from a 16mm reduction negative.
The original aspect ratio of Hogan’s Heroes was 1.33:1, not 16:9, which is equivalent to 1.78:1. There would be no point in shooting for 1.78:1 when all television screens at the time were shaped for 1.33:1 — and would be for decades afterwards.
Wasn’t everything shot on film at that time (short of soaps)? My understanding is that everything now is distributed on tape, so the quality of an old re-run that you see now depends upon the conditions of its transfer.
A rough rule of thumb for 1950s entertainment television is that if the show originated in New York, it was broadcast live. If it originated in Hollywood, it was shot on film. (There were exceptions.) Most 1950s variety series, from Ed Sullivan to Sid Caesar to Milton Berle, were broadcast live from New York.
But your point is still correct — usually the visual quality of a television series originally shot on film comes from the care taken in its tranfer from negative to print, or print to tape.
And so I’d assume that if the transfer was from a print (rather than a negative), it might not look as good (because prints aren’t treated as carefully as negatives).
A lot of 1960s films I’ve seen (in theaters) have a washed-out look. I don’t know if this is because of the quality of the print, or because of the original processing.
All the monitors at the station were RCA. As I recall Bonanza was filmed, but distributed on video tape. Regarding color, the station engineers were required to wear colored shirts should they by accident be on camera.
Color dyes on theatrical print films made by Eastman Kodak from 1952 to 1979 were unstable, and had a slow, sad fade to magenta unless stored under archival conditions (as the camera negatives were — hopefully). Thus, this somewhat extreme example from a 70mm print of Ben-Hur (1959). The bottom frame enlargement, taken from a DVD made from the original negative, by contrast, shows that the problem lies in the print, not the negative.
Another example: a print from the dreadful 1967 “widescreen” version of Gone With the WInd (1939), overlaid on a screen capture taken from the restoration from the original negatives.
During the original network run, Bonanza would have come to the affiliates by a live network feed, not videotape, at least for the Eastern and Central time zones. The network would be broadcasting from a 35mm telecine. A backup 16mm print would be running in synch on a West Coast telecine just in case something should disrupt the East Coast feed to the network of affiliates.
I saw the reels of tape. Perhaps this was later than you speak of.