Well I will be dipped in shit. It wasn’t until they returned home, bemused and annoyed, that the guests discovered the artist had left his mark in them: Their urine had been turned International Klein Blue. Klein couldn’t have been happier. His color had become a part of his guests, just as he wanted it to color the whole world. On April 28, 1958, hundreds of well-heeled Parisians lined up outside the Iris Clert Gallery at 3 Rue des Beaux-Arts, excited to see the newest works by an up-and-coming young artist, Yves Klein. There they were met by two Republican guards standing watch in front of a canopy whose shade was International Klein Blue, a vibrant cousin of cobalt that the artist had invented. While the guests waited to see the exhibit inside, they sipped blue cocktails made of gin and Cointreau, but upon entering, they found only a room with white walls, empty except for a bookshelf. The show was titled “The Specialization of Sensibility in the Raw Material State of Stabilized Pictorial Sensibility,” but it was also known simply as “The Void.”