Fourth class

[…] Mr. S. C. Hawtrey writes that when he knew the Moscow-Kazan Railway (then under British management) in 1913, it was a regular practice in Russia to paint the exterior of first class coaches blue, second class yellow, third class green, and fourth class, where it still survived, brown.

Source: wiktionary

[…] up in front the third and fourth class passengers were making a babel of noise as they either detrained or entrained together with their large families and strange collection of parcels, bundles and earthenware jars.

Source: wiktionary