People wants transparent stuff into the game, but I heard it's difficult to do so, so I have a much simpler solution.
The solution is that on certain sides, or viewed by certain parts (camera or astronauts), that part will be seen as transparent. But from the outside view or by default, that part is seem as not transparent.
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The example of this will be like Kerbal Space Program IVA. Where from the the Kerbal view the blue glass is transparent, while the player see the blue window as not transparent.
@Exo200 maybe a new part with such properties, it may also also resize to align with the surface it is attached on. Making it's properties overlapping the part it's attached to will be great too, no need to make holes for the windows.