Is that really optimal? It is already true in that case that your colour schemes do not work for people with opinionated colour settings. Isn't this just relying on a quirk? The point of not using truecolor is to respect the colour preferences of the user.
XKCD 1172? https://xkcd.com/1172/
It has been working for decades and I would rather have it keep working for decades to come.
What would be optimal is semantic _styles_ (not colors):
- The developer marks the string "XXX" as an error message without even trying to style it.
- The platform/user agent/terminal/whatever displays the string in the default style for "error".
- The user can adjust the theme of their platform/user agent/terminal/whatever to fit their needs/wants.
Semantic styles limit the use - not all interfaces need e.g. "error" context. Take, for example, Task Warrior interface. There is no place for the "error" semantics in it. But there's a place for "critical task" semantics, which is usually also some shade of red.