I just saw this idea at Springwise´s newsletter this morning - and it´s so genius and simple that you can´t help thinking "why did´t anyone think of this before?". Well - it took until the designer Olof Hansson was irritated because the lines on the copy made a mess of his sketch. "It was then that the idea of having white lines hit me. White lines would not be visable on a photocopy, but the dark lines that I had written would." Read more about White Lines great concept here.