a few quotes from the Books....
"The Caste structure is relatively immobile, but is not frozen, and depends on more than birth. For example, if a child in his schooling shows that he can raise Caste, as the expression is, he is permitted to do so. But, similarly, if a child does not show the aptitude expected of his Caste, whether it be, say, that of the Physician or Warrior, he is lowered in Caste."
Tarnsman of Gor pg 42"I knew that the Gorean Caste lines though largely following birth were not inflexible, and that a man who did not care for his Caste might be allowed by the High Council of his city, an approval usually contingent on his qualifications for the work of another Caste and the willingness of the members of the new Caste to accept him as a Caste Brother."
Priest Kings of Gor pg 71"Though one is commonly born into a Caste one is often not permitted to practice the caste craft until a suitable apprenticeship has been served."
Fighting Slave of Gor, pg 209more quotes on Castes can be found here!
~High Castes~
Caste Color Description Initiates white claim to be representatives of the Priest Kings in Gorean Society; and are the religious branch of the Government Scribe blue Concerned with History, accounting, record keeping, etc. Builders Yellow architects, draftsmen, stone masons, etc. Physicians Green practices the Art of Healing Warriors Red infantry, tharlarion cavalry and tarnsmen ~Low Castes~
Caste Color Description Player red/yellow Person Who plays Kaissa professionally Assassin Black Kill for Hire; exists only in Ar. Woodsman brown/black cuts, delivers and works with wood Peasants brown basic Caste of Gor - refer to Themselves as " the ox on which the Homestone rests" Charcoal Makers black/gray mine, process and sell charcoal Tarn Keepers gray/green raise and train tarn Poet/Singer aqua/red Entertainment Pot Maker brown/green much like tinkerers on Urth Saddle Maker tan Leathersmiths Metal Workers gray sword and shield makers, etc. Merchant gold/white merchandising and trading Slaver blue/yellow sub-merchant, sells slaves Lighter green/ white/ red An unknown caste presumably a sub caste of the merchants Bakers gold/white sells baked goods Sleen Trainers brown/gray raise and train sleen Vintners white with green leaves Wine Makers