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Oh hey that was me, artist is りりもん on pixiv, does a lot of Sinnoh.
"Blue" is in reference to Adventures, where she as the third wheel references Blue version for being the third game released, and is switched to Green in official translations. Because Adventures is a concrete story, a lot of Adventures fans treat the colors as proper names, thus Blue to Green is equivalent to Satoshi becoming Ash, i.e incorrect. And two character swapping existing names is easy to follow as far as that goes.
For the game character, I think Green is the easiest going forward given that we have no issue referring to Red and Blue as themselves in different "continuities", and her changes in design are no more drastic than the boys have gotten between games.
