Ever notice some old vinyl records weren't pressed in your basic black?

RCA Victor microgroove (7”-45RPM) colour codes:
Children's – Yellow
Classical – Red
Country & Western – Green
Popular – Black
R&B – Orange
International – Blue

The genre were legacy from 10"-78RPM. Folk was Pop or Country with the occasional R&B. The colour system didn't last long. Materials management & planning nightmare.

When an American library filed their RCA Victor holdings right alongside Columbia & Folkways they used the Dewey Decimal System.

The sorting criteria and genre labels changed because the users changed. The physical inventory remained the same.