We had cable TV in the 1960's in my small town in central IL. Color TV, too - 'bout 1967 or so. The midnight signoffs went on for some time. I remember them going on up into the 70's.
Small market and independent stations did it into the '80s.
I think 1967 was the year we bought our first color TV. If I remember correctly, it was an RCA. The first shows I saw in color was Lost in Space and Family Affair. I can not remember what size it was but I now have a 62" TV with surround sound. Since hubby died, I am giving all the sound equipment to our daughter. They watch a lot of movies and I don't.
The local stations signed off at midnite - 2am while I was in college. This would have been early 90s.
How do I know this? My college didn't have cable.