I'm sure just about everyone watching the downhill skiing has been wondering what's with those blue lines. Here is the scoop.
The two vertical blue lines are intended to give skiers a clear path down the mountain. It's a safety issue. Much like with pre-schoolers and coloring books, there is no penalty for going outside the lines. However, downhill skiers can't stray too far outside because the guide is flush with the limited number of control gates that competitors must pass through. Staying in the middle isn't necessarily the best path.
There are also horizontal lines stretching across the course. Those exist to provide depth perception to the racers. Ever stepped into a snowbank that was a lot deeper than it looked? Now try going downhill at 90 mph and doing the same thing.
Lines are painted before the race by an official wearing a backpack spray tanker. Why blue? Because it pops and looks better than red.