Isn’t #2 the only option?

Websites specifying color for foreground (or background) and assuming browsers will use whatever color they’re expecting for the other has always existed, and still exists

If you’re getting fancy and specifying colors, you can’t cheap out and not specify all colors

If the browser ignores all your colors at that point, then it’s displaying as the user intended If you only specified some of the colors, it’s a bug of the website