I saw it in Xenon and 70mm IMAX. When I saw it in Xenon (i saw xenon after 70mm imax), i noticed the colors were more... microsoft-paint-ish, and the 70mm IMAX was more "vintage" and realistic. Also, some scenes where there's really dark blacks contrasted with bright colors like the scene where the pleasure boat is drifting off into the sunset, the water is very bright in some parts and very dark in some parts, and more saturated (not sure if thats a correct word) or dense; the digital xenon seemed thinner and less dense.
Lol I don't know any cinematography or photography terms, so I might sound like an idiot, but that's how my non-educated self would describe it. I definitely noticed a difference. Also very noticeable was the scenes where theres close-ups or mid-range shots of faces like Kenneth Brannagh or the Spitfire cockpit scenes, the skin color and everything else like the jackets and stuff the colors seemed more realistic and vintage feeling, where digital seemed like the picture was "colored in" with microsoft paint (exaggerated explanation).
By the way, just curious, does this big difference only happen when a film is converted from film to digital? For example, Blade Runner 2049 will be filmed in digital, but I'm guessing it won't have that "colored-in-with-microsoft-paint" look that the xenon conversion Dunkirk had right?
Also, if just for example Nolan filmed all of Dunkirk with digital, would the look of the film watching from xenon look the same in that hypothetically digitally-filmed Dunkirk vs the actual 70mm imax filmed Dunkirk? Or would the colors/saturation/contrast or whatever look better for the digitally-filmed version than the 70mmfilmed version, assuming watching both in a Xenon theater?