The dark blue one is luna, the sister of the White, who's name is Celestia. Celestia is princess of the sun and luna is the princess of the moon. Everyone loved celestial sun and had fun in it every day, but everyone slept through lunas night. Luna thought she wasn't aprecciated, so she transformed into an evil mare of darkness, nightmare moon. She tried to cast the world into eternal night. Because of her crimes, Celestia,regretfully, banished her sister to the moon for a thousand years because of her crimes. Here, Luna and Celestia are battling because Celestia is trying to baish Luna and Luna, obviously, doesn't want that.