The castes are distinguished from each other by size, intelligence, appearance, the color of clothing they wear and the jobs they are assigned to as adults.
Alphas = tall, beautiful, intelligent an wear grey clothing
Betas = Not as tall, but still pretty good looking and intelligent. They wear white clothing.
Deltas = average height and looks, not as intelligent and wear khakis.
Gammas = "Gammas are stupid. They all wear green. . ." (31).
Epsilons = "They're too stupid to be able to read or write. Besides they wear black, which is such a beastly coulour" (30).
The purpose of this class system is to keep everyone under control mentally and physically. People at the bottom of the classes are brain-washed to believe they are at the bottom for a good reason and to accept it. This keeps everyone in his or her own place in society in order for everyone to be happy; therefore, if everyone is happy, then no one will fight and be unhappy (thereby averting things like war).