Depending on their playground status, people who took the bus to school as kids either have fond or not-so-fond memories of that childhood rite of passage: those giant leathery seats, the difficult to open vertical windows, and the flashing red stop sign that stuck out from the driver’s side. Perhaps the most easily recognizable aspect of the school bus is its unique yellow hue, which has remained the same for decades. Just how was this color chosen?

In the late 19th and early 20th centuries, kids came to school in any vehicle that could get them there before the bell rang, whether it was a horse-drawn carriage or a wooden cart on a truck chassis. There was no uniform means of transport, a fact that frustrated both teachers and parents—who were concerned about students’ safety—and the companies that made the vehicles, who needed standardization for mass production (which would enable them to turn a profit).

In 1939, using $5000 in funding from the Rockefeller Foundation and following his own study of school transportation, Columbia University professor Frank Cyr organized a conference at Teachers College on the University’s Manhattan campus. He gathered together engineers and specialists from places like the Ford Motor Company and DuPont to establish national standards for school buses.

The conference created 44 school bus standards, including height and width specifications—and the vehicles’ color. To figure out which hue was best, the group laid out a wide array of shades from light lemon-yellow to dark orange-red along the wall in one of the rooms of Columbia’s Grace Dodge Hall, eventually narrowing the field down to three shades of yellow. Golden yellow was ultimately chosen by the specialists because the distinctive tint—originally called “National School Bus Chrome” and later updated to “National School Bus Glossy Yellow”—is the easiest color to see during the early morning and evening hours when buses operate. Bold black lettering covering the chassis completed the eye-catching look, which Cyr and company hoped would make people more careful when walking or driving near the buses.

Following the conference, the National Institute of Standards and Technology and the National Highway Traffic Safety Administration registered the color in their records as a Federal Standard No. 595a, Color 13432. Initially, about 35 states adhered to the standardization; by 1974, all states used Glossy Yellow on their buses (the lone hold-out was Minnesota, which painted its buses “Minnesota Golden Orange” before making the change).

Buses aren’t the only vehicles to use the distinctive color; you’ll also find it on European mail trucks and cabs buzzing around New York City.