Symbolism, Imagery, Allegory
Fans of South Park can tell you all about the things that get associated with red hair. "Fiery," "temperamental," "ginger"... the list goes on. Red hair is often used in literature to identify a fiery or difficult person and regularly depicts a menacing aura. Naturally, it's the perfect fit for Johnny. Even his make-believe name, "Red Chief" speaks to his feisty nature, and he "puts up a fight like a welter-weight cinnamon bear" (10) just to make sure we know it. Also, note O. Henry's use of the word "cinnamon" here. He's very careful with his word placement and the description keeps Johnny's foremost trait in mind.
Is Johnny's red hair supposed to ease us into the understanding that the boy is essentially a hell-spawn, or simply a clue into his tumultuous behavior? Bill notes:
'There were martyrs in old times . . . that suffered death rather than give up the particular graft they enjoyed. None of 'em ever was subjugated to such supernatural tortures as I have been.' (74)
Perhaps this is a tad hyperbolic, but to poor Bill, this is absolutely the worst experience of his life.
No matter how we approach Johnny, we must consider that his "innocence" is therefore suspect… thanks in no small part to his red hair.