Why are there "shadows" in True Son's happiness at being home with his Indian family? *

Because the "shadows" in True Son's life represent the ending of his happiness with his Indian family when his "adoptive" Indian father forces him to return to his white family.

Explanation: True Son is kidnapped from his white family and adopted by the Delaware Indians, who give him true happiness and make him consider himself as one of them. However, one day his father Cuyloga forces him to return with his white family against his will. In literature, "shadows" are used to represent darkness in the light of a character, they suggest the presence of pain or evil, in this case, being his birth family who he genuinely refuses.