The mystery of the blue lines was the topic of discussion among the television audience of the 2010 Vancouver Winter Olympics. Why were blue lines painted on all the ski slopes? The common conclusion was for decoration; but in fact, the lines served a very serious purpose. The vertical lines running up and down the slope marked the outside boundaries of the ski run. The horizontal lines provided depth perception so a skier could gauge the terrain. Why blue? Because it pops out and looks better than the other Olympic colors of red, yellow, and green.