The late nineteenth century saw large increases in the speed of railroads, the miles of track, and the number and lethality of railroad accidents. When it was found that some accidents were caused by employees who could not detect the colors of railroad signals (red, green, blue and white), railroads began testing applicants for color blindness. This card with pieces of worsted of various colors was used for that purpose. The hand-writing on the back reads "These were the colors chosen at an examination for color blindness by two employees (brothers) of the Amboy [New Jersey] Division, Penna R.R. in 1882 and 1883. J.E. Watkins."
Ref: William Thompson, “Color Blindness Among Railroad Employees,” <i>Popular Science Monthly</i> 31 (Oct. 1887).
