Unrelated: That's how some production facilities record well-running machine configurations. "To run X product, move the rails to the blue marks. To run Y produ

Unrelated: That's how some production facilities record well-running machine configurations. "To run X product, move the rails to the blue marks. To run Y product, move the rails to the red marks." It works okay if the marks are drawn with some level of care... less well when the marks were clearly made in a rush and without a straight-edge. I guess if two people were sharing a bike, they could each pick a color and do the same.