Colour

Many buildings and public spaces in town and cities across the world don't use colour, well not from what I can see from the little bit of research I did looking at images on the internet and at the library. I found some interesting projects where people have used colour and they literally stand out from the crowd of dull and uniform cityscapes. The last image is from a project by Nina Katchadourian where she organised parking by the color of the cars,  there are many more interesting projects at her website.

Image via Urban Design Week

Image and more details via Superflex

Nina Katchadourian

Art in the City II

Some ideas to change how a city looks could be as simple as using colour or coming up with an interesting idea. JR is a French artist who uses cities to show his work and people to inspire it he says his work is about "Raising Questions", see more of his projects here.
The other image is from a favela in Rio de Janeiro, a favela is Brazilian term for a shanty town. More about the project here.

via Favela Painting Project