Much has been said about how Barney Fife in the color episodes was a different character than the black and white ones. He was more Quirky adult than bumbling man-child of the black and white years. Given his character transformation, I've often wondered if one of Barney's guest apperances should have been a repeat of Barney and Thelma Lou Pfffttt! with Andy and Helen being the arguing couple and Barney being the person who needs to settle the dispute. Just think how powerful it would be for Barney to confront Andy and Helen about their bad behavior and be the one to rebuke them instead of the other way around. It would have shown how much Barney had grown as a character working in Raleigh and maybe it would have gotten Andy and Helen to stop bickering as much as they did.

Don Knotts was always willing to play Barney Fife again, if Andy Griffith asked (https://www.metv.com/stories/don-knotts-was-always-willing-to-play-barney-fife-again-if-andy-griffith-asked)

Knotts couldn't say no to Griffith.

It would have been nice if they could have figured out a way for Barney to continue appearing frequently in the color years. Maybe film his segments using the MacMurray method.

It would have been nice if they could have figured out a way for Barney to continue appearing frequently in the color years. Maybe film his segments using the MacMurray method.

Once Jim got the Gomer series, essentially leapfrogging over Don the marketplace was set. To continue with TAGS Don was going to have to get equivalent value. In this case Don and his people defined that as some percentage of ownership in TAGS. Andy and the other TAGS owners had their deal with CBS and it was not contingent on Don being in the cast. So there was really nothing that could be done, the ownership percentage was worth too much, Don was offered a raise but as noted before the market was set.

So in this case the Fred MacMurray solution was not viable, the issue was compensation, not time to do both movies and TV.