When Wilhelm is talking to Simon at the table about their book project he's wearing a green shirt under his jacket but then when he leaves the table and enters his room to throw up, he's now wearing a gray sweatshirt under his jacket.
In the library when Simon goes over to talk to Wilhelm about going to the police to press charges against August, you can see Wilhelm wearing a tan jacket, a green shirt, dark blue jeans and white shoes. After that, when Wilhelm says he's not feeling well and goes back to his dorm, after he closes the door and leans against it, you can see Wilhelm is now wearing the tan jacket, a gray shirt, light blue jeans and black shoes with white soles.