A bit of history. When Henry Ford set up his automobile assembly lines, he used colors to identify different applications for certain parts. The reason was simple, most workers did not know how to read. The use of color codes also "sped up" the assembly lines if you didn't have to read a tag or label, time was money. The practice continued as why fix something that isn't broke. The use of computers in parts management may have reduced the color coding, but not replaced it.
Jim