For “My Three Sons” first five seasons, it was an ABC show. Then they moved to CBS. Why?

The line I have always heard is ABC couldn’t afford to produce it in color, while CBS would. That is certainly believable given their statuses at that time, but I feel there’s more to the story.

ABC did do the final season of Ozzie and Harriet in 1965 in color. But they didn't have a lot in color, including Bewitched--which didn't go color until the next season. So it's possible that's the whole story. They could have run out of budget.