This is actually kind of an embarrassing oversight for a glamour outfit that people have been eagerly anticipating as one of the biggest rewards from this raid series. It feels like they took a modelling shortcut when it came to making the upper chest window and either were in such a rush they didn't test it on anything except white skin, or expected people would somehow not notice.
I'm not even particularly sure if it will be fixed at all, because in order to make see-through cloth (like in the starter Viera chestpiece) they need to remake the model so that the character's skin is actually rendered under the cloth, and then add a semi-transparent texture layer on top of that skin. In the 2B outfit, there's nothing rendered under the flesh-colored cut-outs whatsoever, so fixing this issue means remaking significant parts of the model and of the model's texture, which is the kind of work Square Enix has never done when it comes to models that are already in game: There's models with texture bugs (for example, Lightning's haircut on Miqo'te has messed up specularity that makes the back of your head look like a cracked egg) that have gone unfixed since A Realm Reborn.
Because of this, the 2B outfit, despite being one of the most eagerly anticipated raid rewards for this expansion, will likely look absolutely strange forever unless your character has a light skin color similar to the actual character of 2B. This is terrible, and what's truly most concerning is that Square Enix has a pattern of considering gear models that are already in game to be a done deal, meaning that this game, despite supporting a variety of skin colors that include ones that don't even exist in reality, will forever have this crossover outfit look immersion-breaking for an enormous number of players.