Via Facebook comes this explanation as to how they shot the Giedi Prime scenes for DUNE PART 2 to make it look unique. Turns out that they didn’t shoot it in B&W, exactly:
As epic as its predecessor, Villeneuve’s sequel raises the bar with striking visuals. None is more jaw-dropping than Feyd-Rautha’s (Austin Butler) celebration sequence. The grand fight occurs early on in the film as the Baron Vladimir Harkonnen (Stellan Skarsgard) and Lady Margot Fenring (Lea Seydoux) join the inhabitants of Giedi Prime to watch. It was up to cinematographer Greig Fraser who shot the sequence on black-and-white infrared to deliver Villeneuve’s vision.
Fraser was no stranger to using infrared lighting. He had used it on 2012’s “Zero Dark Thirty” and 2016’s “Rogue One: A Star Wars Story.” “It’s the same light the security camera uses, and you don’t see it. So, my fascination with infrared started because our eyes can’t see it, but the camera can,” says Fraser.
That had a bunch of effects on the footage, ranging from costuming (the costumer had to check every piece of fabric to see how it’d look in infrared) to how the actors’ skin and eyes looked. Having seen it on the big screen… it looked different and interesting and seriously creepy, which I believe was the idea. Getting the mood right for the Harkonnens was something that Villeneuve needed to get right, for reasons that will be obvious by the end of the film…