Sandy,
Regarding England, I know that the Beatles' Magical Mystery Tour was broadcast on the BBC in colo(u)r in 1967 so they must have had it by then...
ABC TV USA demanded that The Avengers be shot in color for the second (filmed) season. They financed some of the show...
Here is more than you would ever want to know about THE AVENGERS!
http://theavengers.tv/forever/