What season did Gunsmoke go to color? The switch came right before CBS nearly killed the show

Gunsmoke went to color in season 12, the 1966–67 season. The first color episode, "Snap Decision," aired September 17, 1966; the season closed with "Nitro (Part 2)" on April 15, 1967. All 29 episodes ran a full hour. Seasons 1 through 11 were black and white, with season 11 the last of them.

The cast at the switch

Season 12 is also a useful marker for the lineup: James Arness as Marshal Matt Dillon, Milburn Stone as Doc, Amanda Blake as Kitty, Ken Curtis as Festus, and Roger Ewing as Thad, under executive producer Philip Leacock and producer John Mantley.

Then CBS pulled the trigger

Ratings had been sliding since the show expanded to an hour. By season 12 it had fallen to roughly 35th in the Nielsens, and a younger group of CBS executives decided a Western from 1955 no longer belonged on the schedule. The producers had their own diagnosis:

The show was a victim of "program fatigue," per the St. James Encyclopedia of Popular Culture.

The reversal came from several directions at once:

• Affiliates — Midwest stations threatened to stop carrying CBS programming entirely.
• Congress — Senator Robert Byrd criticized the decision from the floor.
• Viewers — organized letter-writing campaigns, in volume.
• Babe Paley — the wife of CBS chief William S. Paley, who pressed him personally to overrule his own executives.

What saved it

Paley reinstated the show and moved it from Saturday, where it had lived for 12 seasons, to Monday nights starting in fall 1967. Something had to be cleared to make room, and CBS canceled Gilligan's Island — then still a top-10 show — to do it. Gunsmoke climbed back into the top 10 and stayed on the air until 1975.

For the record: the last black-and-white season produced the show's most decorated hour.

"The Jailer," starring Bette Davis, made TV Guide's list of the 100 Greatest Episodes of All Time.