The author's description of Boo is in entirely white language. My students in a classroom envision Boo as albino. Another feature of his appearance at her first sight is his hidden nature. It is as if he is backed into a corner. I find these features significant because they symbolize how much he wants to stay away from society and the exposure to the effects of society. The white and grey descriptions might also symbolize his innocence at the very least. His hiding away from the light might also be evidence that he knows what he has done is both bad and good. Saving children from a life-threatening destruction is praiseworthy, but having to take a life to do so may not feel very good.
This is the moment Scout has been waiting for since the early chapters of To Kill a Mockingbird. She regrets later that Jem was unconscious and unable to see Boo for himself. Although Boo did not have the huge scars that Jem supposed, nor was he as gigantic as the children imagined, he was a ghostly pale. His hands and face were unusually white from never being exposed to the sun. His eyes were grey and "colorless," and his hair was thin.
You can read the complete description for yourself on the final paragraphs of Chapter 29.
- They were white hands, sickly white hands that have never seen the sun, so white they stood out garishly against the dull cream wall in the dim light of Jem’s room. His face was as white as his hands, but for a shadow on his jutting chin. His cheeks were thin to hollowness; his mouth was wide; there was a shallow, almost delicate indentation at his temples and his gray eyes were so colorless. Scout thought he was blind. His hair was dead and thin almost feathery at the top of his head.