Much has been made of Columbia's “microgroove” but for all the talk about “vinyl” today, the material itself is hardly mentioned in the sources.

Early LPs & EPs (RCA) were pressed in (Union) Carbide and Carbon Corporation 's Vinylite which was marketed, but not specifically formulated, for audio. The initial results were less than desirable and Columbia would eventually switch to Lenahan Associates.

Don't know much about Harry Lenahan except he also had stake in the Somerset Label and the pre-Decca Bill Haley & His Comets.

The competion (RCA's 7”-45RPM) turned to Keysor Resins the first supplier to make application specific vinyl. RCA tried to colour-code the genre for sales clerks & customers:

Black: Popular song
Red: Classical
Dark blue: Popular classical
Yellow: Children’s
Green: Country & western
Cerise: R&B
Sky blue: International.

The “official” system didn't last long. Production/materials scheduling nightmare. Pressing in colour vinyl oth is still a big thing.