But I just found out about it this week.
The mystery is resolved in a passage about "Coronet Blue" from a biography of TV creator and writer Larry Cohen, "The Radical Allegories of an Independent Filmmaker."*
"When the Brodkin Organization took over the series, they wanted to turn it into an anthology...so they played down the amnesia aspect until there was nothing about it at all in the show. It was just Frank Converse wandering from one story to the next with no connective format at all. Anyway, the show ended after seventeen weeks and no one ever found out what 'coronet blue' meant. The actual secret is that Converse was not really an American at all. He was a Russian who had been trained to appear like an American and was sent to the U.S. as a spy. He belonged to a spy unit called "Coronet Blue". He decided to defect, so the Russians tried to kill him before he can give away the identities of the other Soviet agents. And nobody can really identify him because he doesn't exist as an American. "Coronet Blue" was actually an outgrowth of "The Traitor" episode of "The Defenders".
Larry Cohen was the "Coronet Blue" series creator and wrote the episode titled "A Dozen Demons".
*Tony Williams, "Larry Cohen: The Radical Allegories of an Independent Filmmaker" Jefferson, NC. McFarland, 1997