Alexie's adjectives "absolutely true" and "part time" reflect the difficulties of adolescence that Junior experiences.
One of the concepts that Alexie emphasizes in the title is the challenge in growing up Native American. Junior experiences the struggle in being "part time." He does not fit in on the Rez because he possesses hope and belief in the future, elements that do not exist on the reservation. He wants more, something that life on the reservation does not fully encourage. Thus, when he is on the reservation, he feels like a "part time" Native American because he envisions a life outside of it.
When Junior achieves this and goes to Reardan, he experiences racism and prejudice. The school mascot, the denigrating jokes, and his experiencing life as an "outsider" in a largely White setting all reflect how he feels "red" when he among White folks. Reardan is “filled with farmers and rednecks and racist cops who stop every Indian who drives through.” In this light, Junior is "part time" because of the difficulties he faces in a different community. The image of "part time" communicates the difficulty and struggle in Junior's adolescence.
The "absolutely true" image in the title reflects how Junior's narrative is told. Junior's first person narrative enables him to authentically communicate emotional content. Junior speaks with an openness that makes him such a convincing and reliable narrator. The approach Junior takes has been described as "dramatic monologue, verse novel, and standup comedy." All of these are accurate descriptors because all of them are "absolutely true" ways to describe Junior's existence. He experiences different and difficult realities. The common denominator underlying all of them is the honest and "absolutely true" approach he takes in communicating them.