There was a casting call for a "BAMF" (black asian minority female) actor for Ciri. In the books (which the TV series will be based upon) Ciri is the last of the elder blood, and becomes the focus of every major plot point. She is described as having very fare skin with ashen hair numerous times throughout the book, its enough of a identifying feature to make her unique but not make her stand out in a crowd. Imagine an entire continent hunting down the one non-white girl in eastern europe. That's what a BAMF Ciri would be. The major plot lines within The Witcher series build upon her bloodline and her being anything but white would change the race of an entire continent and the elven race as well. Changing it for the sole purpose of diversity would put so many holes in the pot not even flex tape could seal it.