It seems that Dark mode gadget (Special:Preferences#mw-prefsection-gadgets - Dark mode toggle: Enable a toggle for using a light text on dark background color scheme) causes colorshifting in images:

The native dark mode on mobile devices is handled gracefully:

Change 983715 had a related patch set uploaded (by Sergio Gimeno; author: Sergio Gimeno):

[mediawiki/extensions/GrowthExperiments@master] Add mw-no-invert class to background images

https://gerrit.wikimedia.org/r/983715

Thanks for the report. I think this is an occurrence of T345281, fixed adding mw-no-invert class. User impact article thumbnails also present the same problem (with Dark mode gadget, not with the extension). I will ask see if the user impact case makes sense to be solved in the upstream since Codex is already adding a cdx-no-invert class for these.

Change 983715 merged by jenkins-bot:

[mediawiki/extensions/GrowthExperiments@master] Add mw-no-invert class to background images

https://gerrit.wikimedia.org/r/983715

I don't see any dark mode installed in beta, neither gadget or extension 🤔 Do we have an easy way to test this before deployment @Etonkovidova?

In T351097#9419366, @Sgs wrote:

I don't see any dark mode installed in beta, neither gadget or extension 🤔 Do we have an easy way to test this before deployment @Etonkovidova?

testwiki has the Dark mode gadget. And, probably, it's worth to install it on enwiki beta per https://en.wikipedia.org/wiki/Wikipedia:Dark_mode_(gadget).

Checked in testwiki and enwiki wmf.12 - works as expected.