Wait a minute. The guy who wrote the book OWNS THAT CHARACTER. No one else has the right (unless the right has been sold to them) to decide whether the character absolutely has to be read as white.
The idea that readers own fictional characters they did not write themselves is absurd in the extreme.
As a writer, I love that Rick Riodan chose a young black woman to play a character whom he once saw as white. Of course, also as a writer, I know that the character can't be just a mirror image of the original character just with black skin. The character as black would have had significantly different experiences in life that shaped her character and her way of being in the world. The core, of course can be the same, but she is going to have experiences that it is not possible for any white woman to have.
I am looking forward to reading the book and seeing the tv series. Should be a real "mind blower," making readers and viewers think more deeply.