Couple days ago this problem simply popped out of nowhere to me. When using the forced dark theme, there are some images that also have their colors switched, this was not happening before. I formatted my computer last week and it's still happening. I tried updating the browser, using a clean profile directory with no extensions, no flags, nothing different than the standard but it doesn't seem to work properly. Here are some examples:
When it looks like this with dark mode turned off:
Here's a link to the page, but it's not specific to this one, it happens very commonly.
I'm using Windows 10 and most recent Opera GX version (82.0.4227.44).