Paint on walls can be ugly. There are quite a few buildings smeared with paint here in my district, Kreuzberg. Kids smear on walls to leave their signs there (They use the English word “tagging” to describe what they do), to demonstrate that they are somebody.
On the other side paint on walls can be very nice, can be art. The photo above show a house five minutes away from where I live. It has got mural paintings all over, and it has got a strip on the wall which is free for anybody to spray their colours on. I often see them working there, having something painted on a piece of paper and now trying to transfer it to the bigger space on the wall. Every two weeks or so this strip is painted over with white paint, in order to offer a new space for a new group of artists.