However, cadmium is also an expensive and toxic heavy metal, so now many saturated-color pigments are now azo-based organics.

In April 1939, Frank W. Cyr, a professor at Teachers College, Columbia University, in New York, organized a conference that established 44 uniform national design, construction, and safety standards for school buses in America, including the exterior body color.

[4] The yellow-orange color was selected because black lettering on it was most legible in semi-darkness,[4] and because it was conspicuous at a distance and unusual enough to become associated with school buses and groups of children en route.

North American-style yellow school buses are being introduced in some parts of the United Kingdom, prompted by corporate links to the American industry, for example First Student UK, or a desire to re-brand school buses, such as West Yorkshire Metro's Mybus.

[citation needed] Yellow school buses are becoming more prevalent in Australia, e.g. in and around Adelaide.