Telika: I'm not familiar enough with The Witcher to know how important and how explicit the "racial" traits of its characters are. From what I understand, it's a fantasy world, so it's not exactly the same as anachronic northern gaul diversities in an Asterix adaptation or african re-casts in homerian mythology.
Thing is, even if there are reasons to roll eyes (if the books are super specifically super importantly defined by the phenotypical realities of a given region in a given moment of history), I also note that the internet outrage mostly comes from the same people who were also shedding tears of blood at the skin colour change of marvel characters or at the "sudden" inclusion of women and blacks in the star wars universe, so, yeah, limited credibility.
Still :
Just wanted to put it in the broader context of tv series adaptations. Books being mangled for the tv screen is the rule. They're adaptation, not transposition. Adaptation to a different media, adaptation to a different public, adaptation to different intents. It's a reappropriation, really, always closer to "inspired by" than to "transcribed from". As such, the level of faithfulness is always cringeworthy for fans of the original source. I mean, do "Walking Dead" readers watch the "Walking Dead" series ? What do they recognize in it ? What about miniseries like Le Carré's "The night manager" ? Or Sherlock Holmes stories ?
They're always their own thing, in their own universe. I'm not particularly interested in The Witcher (maybe it'll change if I play the game some day), but, good or bad, I wouldn't assume this series to be representing the novels or the books. Like Stalker, it will be -and kinda has to be- three strories in three distinct worlds, sharing some names and vague concepts. Given that, making a big deal of some secondary character's skin colour in particular is futile.
But of course, we know it's not about adaptation faithfulness. It's, magically, only when a change pertains to skin colour or minority representations that you get such outrage. Which aspects of adaptations are such big stakes on the internet is not random.
Yeah how dare all those racists expect a faithful take on the books. Conversely, when casting a minority in place of a white actor, it's considered stunning and brave.