The Media Laboratory's western wall has a distinctive tile pattern, with three unique sets of colored tiles. The artist Noland set them in a specific order --- black, red, yellow, from north to south (left to right). Most people apparently don't know the order of these colors (and occasionally a nearby undergraduate living group would paint a fourth green square on the wall (see J. IHTFP p. 22)).
One morning in September, the squares traded colors, becoming yellow, black, and red, in order.
Numerous people apparently walked by without a second glance. Unfortunately, the morning sun seemed to adversely affect the new colors, causing some of them to fall off. (In fact, for a while, the squares were yellow, red, and red, in that order). Apparently, the new colors were flat pieces of wood painted to match the Media Lab's wall, and attached with adhesive. Finally, the squares were removed. One must wonder, though, if the squares had stayed up, how many people would have noticed the difference?