I don't want to get into an argument about 'true' colour of TIEs, but all the fighters were repainted for Empire & Jedi
Here's an image from the ESB section of the recent Chronicles book, translated text says
"It was discovered that the paint for the Tie Fighter's body color, which was custom-ordered in the previous work, was almost the same color as commercially available paint for models, and all Tie Fighter miniatures were repainted with it."
The two images of the ESB TIE look totally different in a change of lighting
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Vaders TIE was not repainted, this is the Studio model, the two photos taken in the same photoshoot
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Here's a Korbanth TIE Bomber kit I painted with ArchiveX Stormy Sea, different lighting, different effect
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My thoughts on the subject, I think George wanted the Imperial fighters in the Blue/grey,..lighting & keying took the blue colour out of how the ships looked in ANH, but he persisted & pushed ILM to get the colour he wanted to appear on screen for the sequels
BUT as I said earlier,....my Bandai Vader & wingmen set, I hope to lighten the Stormy Sea to make them more like they are on screen in ANH
J