To understand much of our language, Gnorts would have to already be aware that our words and symbols gain meaning from how they're used, and you couldn't, for instance, determine that a swastika is offensive (in the west) by its shape alone.
In this case, the term "colored people" gained racist connotations from its history of being used for discrimination and segregation - and avoiding it for that reason is the primary principle at play. There's also the secondary/less universal principle of preferring "person-first language".
They would instead have a history and culture (or many histories and many cultures) to learn in order to contextualize words and symbols and find their actual meaning, because meaning doesn't really exist without context.
We all know what's going to happen. The underlying history and culture would change within the span of 24 hours, and suddenly "colored people" would loose it's racist connotations.
Awareness of history and culture won't help you understand language rules. Instead, to avoid saying something racist, one must be keenly aware of political expediency.