You'll have to wait until night falls in Seville to try this out.
Colour By Numbers is a light installation in Seville's Tower of Perdigones. The creators of CBN did a similar installation a couple of years back in Stockholm.
The way it works is this: Using your cellphone, you call the number listed on the website and then get to control the color of the lights on each floor of the tower, watching the result via a live feed on your computer. The installation only works when it's dark in the host country. Cost is equivalent to an overseas call to a cellphone. Details are on the Colour by Numbers website, which has been up and down this morning.