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.