Oddworld Artbook posted:

As the game design evolved, it became apparent that different classes of Mudokons were needed. To distinguish these classes Lorne suggested we have Mudokons grow feathers are they become more spiritual. These feathers become much like headdresses used in ancient cultures to represent status. So a Mudokon who was a slave to industry, like a scrub, would not have any feathers. But a powerful shaman, who is at the spiritual apex of the Mudokon culture, would have a full decorative headdress made of feathers. The warrior and mudokon shaman feel like they have painted themselves in various colors to give them a tribal and distinctive feel.