What makes Mr. Jamison an unusual character in "Roll of Thunder, Hear My Cry"?

Mr. Jamison is an unusual character because, in the atmosphere of prejudice and intolerance that exists in Mississippi in the 1930s, he is a white man who treats the Logan family with dignity and respect.  Cassie says,

"I liked Mr. Jamison and I didn't mind admitting it...he was the only white man I had ever heard address Mama and Big Ma as 'Missus', and I liked him for it...Besides that, in his way he was like Papa...ask him a question and he would give it to you straight with none of this pussy-footing-around business...I liked that" (Chapter 5).

Mr. Jamison is the attorney from whom the Logans purchased their land.  He willingly helps them with the legal work involving their holdings, arranges for them to obtain credit in Vicksburg during the sharecroppers' boycott, stands up to a white mob in an attempt to prevent T.J.'s lynching, and sagely advises Paul Edward to remain silent about his part in diverting attention away from T.J. by setting the fire in the cotton field.  Mr. Avery's honesty and fairness contrast sharply with the attributes of some other white characters in the novel, such as Harlan Granger, who wants to acquire the Logan's land, the children at the store who shame Big Ma by putting her in a situation where she must tolerate their demeaning behavior, and Lillian Jean Simms, who believes that, because of the color of her skin, Cassie exists to be subservient to her and meet her needs.