The prank was simple and brilliant. DHL hired companies like UPS and TNT to deliver large black boxes to addresses that were particularly difficult to find. But the boxes weren’t actually black. Instead, they were covered with a temperature-activated ink that appeared black when the boxes were chilled to sub-zero temperatures at the time of pickup. But as they warmed up in the back of delivery trucks, the black ink faded revealing a large message on the side of the boxes boasting that “DHL is faster.”
Gizmodo