>>53075585That's because Blue is her original Japanese name. The Japanese names for the gen 1 protagonist and rival are Red and Green, after the original Japanese gen 1 versions, but since the international release of gen 1 was called Red and Blue the rival's name in the rest of the world was changed to Blue. That caused an issue when they actually introduced a character called Blue in Japan. The game translations just swapped her and Green's name because they didn't want to retcon the gen 1 rival's name, while Pokemon Adventures manga just used the original Japanese names.
The gen 1 rival being Green in Japan is also why Leaf is called Leaf. Since the male protagonist was already called Red GF wanted to keep the theme and name the female protagonist introduced in FR/LG after the other version of the game, but since Green was already taken by the rival they called her Leaf instead, from Leaf Green.
