I'm of the belief that wherever I live, it must feel like home.
So, back in the day when I rented, I did whatever was allowed/I could get away with. The first flat j had on my one had the walls papered...with pretty wrapping paper. Later, with partner/ husband...walls were painted in deep shades...navy blue, olive green, red. Maybe we were lucky to have easy going landlords...though I don't even remember asking. A bathroom git papered in blue/silver paper...very 70s! This was 30-40 years ago in Manhattan and Brooklyn. I get the impression landlords are far less permissive now. Leases then were also a minimum of 1 year...sometimes 2.