We never really know what Boo looks like until the final chapters of To Kill a Mockingbird. Jem, Scout and Dill spend much time discussing how he must look. Jem decides that he is six and a half feet tall, has a huge scar on his face and that his hands are always bloody from eating raw squirrels. However, Scout finally gets to see him in Chapter 29. As the children had imagined, Boo is extraordinarily pale from the lack of sunlight.
They were white hands, sickly white hands that had never seen the sun, so white they stood out garishly against the dull cream wall in the dim light of Jem's room... my eyes travelled up his thin frame... His face was as white as his hands... His cheeks were thin to hollowness; his mouth was wide... and his grey eyes were so colorless I thought he was blind. His hair was dead and thin, almost feathery on top of his head.