Question

why are school buses of yellow colour mostly

Answer 1

Federal law in the United States requires that, in addition to flashing lights and safety devices,school buses must be painted “school bus yellow." Before thestandard school bus yellow color was developed, school buses were a pure yellow, closer to the color of a lemon.

Answer 2

School bus yellow. School bus yellow is a color which was especially formulated for use on school buses in North America in 1939. ... It became known officially as "NationalSchool Bus Chrome".