L'art de coleur is a color panel with a small brush for the sapping slot of the spy. It's an alternative for destroying enemy building by painting enemy sentries into his own color to convert it. It works for every kind of building. A full-painted sentry works against his creator, a colored dispenser gives friendly units more profit and teleporters just won't work. The Engineer can't destroy these buildings with the self-destruction anymore, but he can build new buildings instead. But it's really hard to convert enemy buildings. It's even harder than destroying them. You have to stay right by the building while you're coloring it. If you cancel because of an enemy, you have to start over. And of course an engineer always got a sense for his buildings: "SPY PAINTING MY SENTRY!". It takes the same time like a building needs to get destructed with a sapper. In other words, even other classes can block your action by killing you.