(WHTM/NEXSTAR) — You probably see school buses out and about pretty much every day when school is in session. But have you wondered why school buses are yellow and not a color like bright green?

It’s not for looks or because the U.S. Department of Education loves the color yellow — it’s more about science and safety.

According to the Children’s Museum of Indianapolis, the practice dates back to 1939, when Frank W. Cyr, also known as the “father of the school bus,” held a conference for transportation officials, educators, and even paint experts.

The year before, Cyr had done his own research and found out there were no standards for the color of school transportation. Smithsonian Magazine explains Cyr studied buses in 10 states and realized kids were riding to school in buses of all different colors, including colors of the U.S. flag.

“Red, white and blue was camouflage if you think about it. It was to make kids patriotic,” Cyr said at a 50th-anniversary celebration, as reported by the Los Angeles Times. “It was well-meaning, but they made the buses less visible. And I don’t think it really had much effect on patriotism.”

The conference was held for seven days, and a 42-page construction guide for buses was created. While the standardization of U.S. school buses was promoted for safety, the decision was also — naturally — one of economics. With more standardized looks, buses could be mass manufactured and thus cheaper to make.

The guide contained the standardized yellow paint color: “National School Bus Chrome.” That particular shade of school bus chrome was a pure bright yellow, closer to the color of a lemon. Over time, however, the yellow was softened and became a bit warmer. 

School buses are a mixture of yellow and orange, almost like the color of the inside of a mango. (Getty Images)

Today, the color is known as “National School Bus Glossy Yellow,” as explained by the National Highway Traffic and Safety Administration.

According to scientific research from the Color Matters website, the color yellow gets your attention more than any other color. Even when you’re looking forward, it’s easier to see yellow in your peripheral vision. Scientists say that lateral peripheral vision for detecting the color yellow is 1.24 greater than that of the color red.

But even though most school buses are yellow, they’re not required to be yellow. The NHTSA explains there’s no federal requirement on bus color and that state and local governments create their own rules on the matter. It is recommended, however, that they be yellow.

“The uniformity of school bus appearance helps motorists identify the vehicles as school buses,” the NHTSA says.

There’s also no specification about how many people can safely sit inside a bus, which is also left to local schools and governments. The NHTSA recommends that all students should be able to be fully seated while the bus is in motion.

What happened to the ‘chrome’?

In case you’re wondering why “National School Bus Chrome” changed over the years to “National School Bus Glossy Yellow,” it’s not just that the shade of yellow evolved.

The “chrome” contained in the original name was in reference to the metal chromium, which the paint used to contain. As Gizmodo explains, this particular metal — hexavalent chromium — was widely used in manufacturing before its toxicity (and cancer-causing potential) was discovered.