This question occurred to me when watching Dune: Part Two, where Giedi Prime is depicted as an almost completely grayscale environment. While the movie doesn't explain how this effect occurs, it's an actual effect noticed by the characters.
This trope doesn't seem to be particularly common so I wonder which production came up with it first.
TVTropes has a Deliberately Monochrome trope page, but most of their examples use monochrome as a stylistic choice only. (To be honest, though, I didn't go through every single one of their long list of examples.)
What I'm looking for:
- The monochrome environment is an actual part of the plot or story, not just a stylistic choice or an artistic element. For example, Sepia Kansas from The Wizard of Oz doesn't count.
- The monochrome environment must be pervasive, affecting people and things introduced into it more than just a trick of the light. For example, simple night or darkroom scenes do not count. It should be some magical or technological effect actively affecting everything, except maybe special characters or objects resistant to it.
What I have found so far:
- Live-Action TV: Star Trek: Voyager has Captain Proton, first shown in the 1998 episode Night. While Captain Proton is a (fictional) 1930ish show originally shot in black-and-white, the Voyager holodeck recreation is programmed to remove all colors (including The Doctor's, who is rudely monochromized by Ensign Kim).
- Live-Action Film: The 2004 movie The Trixxer features a location called BlackWhite Castle, one of the last castles in England still black-and-white. This example is somewhat borderline since the movie's intention is to lampoon 1960s Edgar-Wallace-style crime films rather than be a fantasy movie, but within the movie it's an actual magical effect noticed by the characters.
- Animation: Not sure. The 1968 animation Yellow Submarine comes pretty close, but the result of the Blue Meanies invasion is not fully monochrome and it's not a pervasive effect after the fact.
Surely there must be earlier examples.