In cities across the globe, color-changing lights on buildings and towers are used to celebrate everything from the Fourth of July to St. Patrick’s Day, but the permanent light installation Colour by Numbers in Stockholm’s Telefonplan tower may be the only one in the world that can be controlled by anyone with a phone.

Installed in 2006, the rainbow-colored installation uses the windows in the upper portion of the 20-story spire to project whatever hue is ordered up by people via a smartphone app. Either standing on site or even through a streaming webcam, amateur painters of light who want to make their temporary mark on the Stockholm skyline can choose which floor they would like to color and then create a custom color using a mixable RGB interface. Even without a smartphone, people can call a free number and paint the tower using just their keypad.

The tower’s lights can be seen from all around southern Stockholm and the creators hope that the work can stand as a statement on the power of democracy and the power of the public. On some level this installation is successful in this endeavor, but it is also simply a cool bit of city-hacking that can make citizens and visitors alike connect with an often alienating urban environment.