RCA C73685 Developmental 21 Inch Color Tube
This tube has a 14 pin base like the one on the 19VP22 and 7JP4. According to Chuck Azzalina, the number corresponds to tubes made in 1957. RCA started using glass tubes in that year, so this tube probably had experimental phosphors or guns.
The tube was in the collection of the Sarnoff Library and was donated to the Early Television Museum when the library closed. Thanks to Dave Sica and John Tyminski for rescuing it and delivering it to the museum.