The nicknames for different characters are an indication of personality traits. Shug is named for Sugar because she’s so desirable. (Her real name is Lillie). Squeak is nicknamed Squeak because she’s mousy and lets Harpo push her around. But even Squeak gets everyone to call her by her real name, Mary Agnes. Mr.__ is called by the honorific "Mr.__" only until Celie recognizes her own dignity and worth alongside of him. Then she starts calling him Albert.
For the female characters in particular, occupation says a lot about their levels of control over their lives. Celie’s lack of a position as anything other than a wife renders her powerless. Shug and Squeak, who have voices and can make money singing, are given power to go where they want, when they want, and with the people they want. Sofia’s role as maid in the mayor’s house makes her like Celie – powerless. Nettie’s job as a missionary and teacher makes her an independent woman. In addition, Celie gains more control over her life when she starts her own business making pants.
Celie is originally downtrodden and this is represented accurately through her clothing. When Mr.__’s sisters visit, they’re horrified to find her wearing rags and they goad Mr.__ into buying her some new clothes. Shug’s power and independence is represented by the beautiful and sexy clothing she’s able to wear. Finally, when Celie starts wearing pants, it also symbolizes a change in her relationship with men, especially Pa and Mr.__.
Celie uses very rural, Southern speech (for example, instead of using the word "ask," Celie consistently uses "ast"). The effect of this dialogue is to put us right in the middle of Celie’s world – a black, rural, largely uneducated world. Nettie’s narration is contrasted with Celie’s. It’s clear from Nettie’s diction that she has received more education and is working as a teacher. It’s closer to Standard Written English. Her diction indicates a difference in the sisters’ levels of education and experiences of the world.