How does the author describe Boo’s appearance after Scout points him out?

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.