Pokémon Blue Version is the international version of Pocket Monsters Midori. Compared to the earlier version, Blue has updated graphics and audio, some changes to area layouts, and significantly overhauled code, all of which in fact originate from the Japanese release of Pocket Monsters Ao.
Blue and Midori share the same version-exclusive Pokémon; in order to complete the Pokédex, players must trade with owners of Red version.
