Why is the main character invisible in college ?

The central conceit in Ralph Ellison’s Invisible Man is that the unnamed narrator of the tale is figuratively invisible to the larger American society because he is a young black man. Therefore, he is not only “invisible” in college, but also throughout the rest of the novel. He considers himself an invisible man because he is marginalized; he is pushed aside and disregarded by a racially stratified American society, and he considers himself unseen. Indeed, his time in college contributes to his designation as an invisible man. After he has allowed a wealthy, white supporter of the college, Mr. Norton, to see the darker side of the town, Dr. Bledsoe is furious with the narrator. Dr. Bledsoe berates the narrator in a way that exposes his own manipulative personality:

“You're nobody son. You don't exist--can't you see that? The white folk tell everybody what to think-- except men like me” (143).

Dr. Bledsoe confirms the narrator’s marginalized status here. Thus, the narrator is indeed metaphorically invisible in college, and he remains this way throughout the remainder of the novel.