The Collaborative International Dictionary of English v.0.48:

Whiteboy \White"boy`\, n.
   1. A favorite. [Obs.] See White, a., 6. "One of God's
      whiteboys." --Bunyan.
      [1913 Webster]

   2. One of an association of poor Roman catholics which arose
      in Ireland about 1760, ostensibly to resist the collection
      of tithes, the members of which were so called from the
      white shirts they wore in their nocturnal raids.
      [1913 Webster]