I was watching a movie called "Starred Up" The movie is in a prison
in the UK. The walls are painted up to 5 feet (1.5 meters) dark green
and then light green to the ceiling.

I had just seen a documentary a few weeks ago where somewhere in
Russia they were studding some propaganda films and the walls of the
film room were also painted the same way.

Other than just plain aesthetics, would there be a reason for that?