During the 1954-1955 TV season, Bill Paley had a number of shows film single episodes for broadcast in color, long before that became the industry standard later in the sixties. I had always known Burns and Allen did one of these, which was very costly at the time. I've never seen the full thing, but you can catch a clip of the color footage from a CBS anniversary special in a segment on Paley here (The B&A clip starts at 7:40). This is probably some of the ONLY color footage of Gracie known to exist, but the episode was always syndicated with a black and white copy.
According to this Lucy Fan site, the March 6, 1955 ("Jack Takes the Beavers to the Fair") was also originally done as part of this color broadcast test program. Is this information accurate? And, if the B&A color footage still exists, might the Jack Benny show in color exist too? That would be a great addition to an eventual official DVD release of the show (and B&A too!) ... (sigh) someday!