> The best rule of thumb is, if you’re not sure whether something needs to be said right now, hold off and see what happens. You can always say it later if it turns out there’s no way for the conversation to move forward without your correction.

From the context, it sounds like it's not so much about "don't correct people" as much as it's about "don't uselessly correct someone to showcase your own knowledge and not advance the conversation".

> A well-actually is when you correct someone about something that’s not relevant to the conversation or tangential to what they’re trying to say.

So, as long as the conversation is about the colour of the sky, (or about green things) you can just answer it.